SmartNano

Emerging pollutants, such as microplastics (MPs), are becoming a significant issue worldwide. The highest percentage of MPs released into the environment occurs through daily laundry. The average weight of dreg obtained from 5 kg of laundry was 1.26 g/kg. According to energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA) analyses, the dreg consisted of MPs (78.3–89 wt%, organic elements: C/O) and alien materials (11–21.7 wt%, inorganic elements: Al/Fe/Ca, etc.). Thus, to reproduce the real environment, alien materials (Fe3O4 and CaCO3) were added to various types of model MPs in the presence and absence of sodium dodecyl benzenesulfonate (SDBS) to test MP removal. Hydrophobic and hydrophilic MPs were generated upon laundering, accounting for 55–59% and 41–45% of MPs, respectively. We provide a novel approach to design a laundry filter system for the simultaneous removal of SDBS and hydrophilic/hydrophobic MPs.

A scoop net equipped with an underwater anti-oil-fouling (AOF) filter was tested for the cleanup of low-sulfur fuel (LSF) in support of a landmark decision made by the International Maritime Organization (IMO) in 2020. An underwater AOF filter (fabric/O-CS/PVA-KGM) possessing a partially dissoluble surface was prepared by the stepwise coating of oxidized carbon soot (O-CS) and polyvinyl alcohol/Konjac glucommannan (PVA/KGM) onto different fabrics. The effects of the molecular weight (MW) of PVA, thickness of the filter, and water temperature on the underwater AOF performance of the filter were investigated. Since the fabric (3 mm)/O-CS/L-PVA-KGM filter showed the highest water absorption capacity (6.23 g/g) and water content (96.4%) after 1 h, this filter showed the lowest amount of residual LSF (Abs: 0.004 at 275 nm) and the best long-term AOF stability after 30 cycles at 20 °C. This filter still showed excellent AOF performance (Abs: 0.008 at 275 nm) and high flux (66,793 L/m2h) at 4 °C due to high water absorption capacity/contents and large pores/relatively long multichannels, respectively.

Chemical water pollution poses a threat to human beings and ecological systems. The purification of water to remove toxic organic and inorganic pollutants is essential for a safe society and a clean environment. Adsorption-based water treatment is considered one of the most effective and economic technologies designed to remove toxic substances. In this article, we review the recent progress in the field of nanostructured materials used for water purification, particularly those used for the adsorption of heavy metal ions and organic dyes. This review includes a range of nanostructured materials such as metal-based nanoparticles, polymer-based nanomaterials, carbon nanomaterials, bio-mass materials, and other types of nanostructured materials. Finally, the current challenges in the fields of adsorption of toxic materials using nanostructured materials are briefly discussed.

A solar-driven unmanned hazardous and noxious substance (HNS) trapping device that can absorb, evaporate, condense, and collect HNSs was prepared. The HNS trapping device was composed of three parts: a reverse piloti structure (RPS) for absorption and evaporation of HNSs, Al mirrors with optimized angles for focusing light, and a cooling line system for the condensation of HNSs. The RPS was fabricated by assembling a lower rectangle structure and an upper hollow column. The lower rectangular structure showed a toluene evaporation rate of 6.31 kg/m2 h, which was significantly increased by the installation of the upper hollow column (11.21 kg/m2 h) and led to the formation of the RPS. The installation of Al mirrors on the RPS could further enhance the evaporation rate by 9.1% (12.28 kg/m2 h). The RPS system equipped with an Al mirror could rapidly remove toluene, xylene, and toluene–xylene with high evaporation rates (12.28–8.37 kg/m2 h) and could effectively collect these substances with high efficiencies (81–65%) in an unmanned HNS trapping device. This prototype HNS trapping device works perfectly without human involvement, does not need electricity, and thus is suitable for fast cleanup and collection of HNSs in the ocean.

A tower air filtration system was designed in which bead air filters (BAFs) were actively rotated by a fan motor to remove particulate matter (PM) or HCHO gas. Three types of BAF, hydrophilic, hydrophobic, and hybrid, were prepared and compared for the removal of PM and HCHO gas. A tower air filtration system loaded with hybrid BAFs purified 3.73 L of PM (2500 μg/m3 PM2.5) at a high flow rate of 3.4 m/s with high removal efficiency (99.4% for PM2.5) and a low pressure drop (19 Pa) in 6 min. Against our expectations, the PM2.5 removal efficiency slightly increased as the air velocity increased. The hybrid BAF-200 showed excellent recyclability up to 50 cycles with high removal efficiencies (99.4–93.4% for PM2.5). Furthermore, hydrophilic BAF-200 could permanently remove 3.73 L of HCHO gas (4.87 ppm) and return the atmosphere to safe levels (0.41–0.31 ppm) within 60 min without any desorption of HCHO gas.

A ubiquitous material (sponge or cotton fabric)-based Janus air filter (JAF) with an optimized ratio of hydrophilic (75%) and hydrophobic (25%) parts was prepared using a simple and economical process that did not require specialized equipment or multiple steps. As a result of the hydrophobic part of the JAF, the adsorption of particulate matter (PM) was higher at the rear than at the front of the hydrophilic part of the JAF. The amount of PM adsorbed was further increased in the hydrophilic part of the JAF when the degree of hydrophobicity was increased in the hydrophobic part. The sponge/cotton JAFs exhibited excellent recyclability of up to 30 cycles with consistent long-term performance (RE: 99.99% and △P: 61 Pa) at extremely high PM2.5 concentrations (over 624,230 μg/m3) and air velocities (1.05 m/s). A modular JAF could achieve the performance of 99.89% at a PM0.3 concentration of 999 μg/m3 and air velocity of 1.05 m/s with a low pressure drop of 152 Pa.

Nanomaterials that can be reversibly or irreversibly changed in structures and properties by the influence of external chemical and physical stimuli are defined as smart nanomaterials. External chemical and physical stimuli can include pH, temperature, moisture, force, electric fields, and magnetic fields. Smart nanomaterials have been used for environmental remediation, energy generation, 3D printing, smart textiles, self-healing, and healthcare. Since oily wastewater, wastewater, and polluted air result in serious health and environmental problems, significant interest has been focused on environmental remediation using smart nanomaterials. The aim of environmental remediation using smart nanomaterials is to remove contaminants from environmental media such as groundwater, surface water, sea water soil, or air. This Special Issue deals with the recent progresses in smart nanomaterials and related nanomaterials for environmental remediation. Our Special Issue is composed of five main topics, such as oil/water separators, adsorbents/absorbents, catalysts, and fundamental studies for environmental remediation. Herein, I summarize each topic discussed in our Special Issue. This editorial begins with oil/water separators for the separation of water or oil in oil or water, respectively. Then, adsorbents/absorbents, air filters, and catalysts are presented. Finally, fundamental studies for environmental remediation are discussed.

A wastepaper (WP)-based cylindrical hollow air filter (CHAF) is prepared by oxidative heat treatment of WP fragments, followed by vacuum filtration of a WP solution to form a WP column that underwent boring. The CHAF shows excellent PM2.5 removal efficiency (99.12%) and an extremely low pressure drop (4 Pa) at a flow rate of 1.5 m/s because of the structural and chemical characteristics of the CHAF. CHAFs that are connected in series and parallel demonstrate the advantages of an increased removal efficiency and a decreased pressure drop, respectively. Thus, combinations of CHAFs connected in series and parallel further increase the PM2.5 removal efficiency and decrease the pressure drop at a high PM2.5 concentration of 644,000 μg/m3 and a high flow rate of 5–10 m/s. The CHAFs are also able to simultaneously remove particulate matter (PM) and formaldehyde (HCHO) at very low concentration levels (below 0.1 ppm). A miniature air cleaner equipped with the CHAF can effectively remove 5 L of PM2.5 at extremely high concentrations of over 650,000 μg/m3 and a high flow rate of 5 m/s with a high efficiency (99.24–96.88%), low pressure drop (31–34 Pa), and short removal time (3.5 min) for up to 270 cycles.

Air and water pollution pose an enormous threat to human health and ecosystems. In particular, particulate matter (PM) and oily wastewater can cause serious environmental and health concerns. Thus, controlling PM and oily wastewater has been a great challenge. Various techniques have been reported to effectively remove PM particles and purify oily wastewater. In this article, we provide a review of the recent advancements in air filtration and oil/water separation using two- and three-dimensional (2D and 3D) bulk materials. Our review covers the advantages, characteristics, limitations, and challenges of air filters and oil/water separators using 2D and 3D bulk materials. In each section, we present representative works in detail and describe the concepts, backgrounds, employed materials, fabrication methods, and characteristics of 2D and 3D bulk material-based air filters and oil/water separators. Finally, the challenges, technical problems, and future research directions are briefly discussed for each section.

Magnetic sponges (MSs) and magnetic threads with hydrophilic and hydrophobic characteristics that can perform remote-controlled oil/water separation in a confined space and anaerobic reactions were prepared. For large amounts of water or oil, trainlike hydrophilic or hydrophobic MSs composed of more than three sponge balls moved as a group and quickly absorbed the water or oil droplets in oil or water by magnetic manipulation from outside of the tube. For the removal of heavy oils below the water in three-liquid multiphase solutions, the hydrophobic MS balls were moved to the heavy oil below the water, absorbed some of the heavy oil, and returned to the light oil layer to deliver the heavy oil by means of an external magnetic field. The mixed oils floating on the water were easily removed by a suction pump once the heavy oil had been completely delivered to the light oil layer via the round-trip process. Furthermore, our approach was demonstrated for use in an anaerobic reaction system due to the strong magnetic property that transfers the reactants/products, the porous structure providing a reaction site, and the prewetting ability containing the reactants/products of the MSs and the oil layer prohibiting oxygen contact.

There is significant interest in developing novel absorbents for hazardous material cleanup. Iron oxide-coated melamine formaldehyde sponge (MFS/IO) absorbents with various IO layer thicknesses were synthesized. Various other absorbents were also synthesized and compared to evaluate the absorption capability of the MFS/IO absorbents for strong acid (15%, v/v) and base (50%, m/m) solutions. Specifically, absorbent and solution drop tests, dust tests, and droplet fragment tests were performed. Among the various absorbents, MFS/IO absorbents possessing a needlelike surface morphology showed several unique characteristics not observed in other absorbents. The MFS/IO absorbents naturally absorbed a strong base solution (absorption time: 0.71–0.5 s, absorption capacity: 10,000–34,000%) without an additional external force and immediately absorbed a strong acid solution (0.31–0.43 s, 9830–10,810%) without absorption delay/overflow during absorbent and solution drop tests, respectively. The MFS/IO absorbents were also demonstrated to be ideal absorbents that generated fewer dust particles (semiclass 1 (ISO 3) level of 280 piece/L) than the level of a clean room (class 100). Furthermore, the MFS/IO absorbents were able to prevent the formation of droplet fragments and solution overflow during the solution drop test due to their unique surface morphology and extremely high absorption speed/capacity, respectively.

In this work, we report a feasible fabrication of NiCo2S4 nanotree-like structures grown from the Ni nanoparticle (NP)-doped reduced graphene oxides (Ni-rGO) by a simple hydrothermal method. It is found that the presence of Ni NPs on the surface of the rGOs initiates growth of the NiCo2S4 nanotree flocks with enhanced interfacial compatibility, providing excellent cyclic stability and rate performance. The resulting NiCo2S4/Ni-rGO nanocomposites exhibit a superior rate performance, demonstrating 91.6% capacity retention even after 10,000 cycles of charge/discharge tests.

Ultralight sponges with the ability to release protons on demand, namely, superhydrophobic melamine formaldehyde sponges (SHpho-MFSs), which are characterized as being safe-to-handle, convenient-to-use, easy-to-store, easy-to-carry, and easy-to-collect, are switched from superhydrophilic MFSs (SHphi-MFSs) by a one-step ultrasound treatment at a low pH. The wettability of the SHphi-MFS is completely switched from the outside to the inside of the MFS. After wettability switching is achieved, the SHpho-MFS that is prewetted with water and oil is able to selectively separate both water and oil, respectively. A compressed SHpho-MFS also exhibits excellent separation performance of a water-in-oil emulsion. Furthermore, since the SHpho-MFS can linearly release protons in an aqueous solution, during the oil/water separation (water-removing), an aqueous solution of a strong base is neutralized or changed into a certain solution with a tailored pH by a simple filtration step using an appropriately sized SHpho-MFS. The SHpho-MFS can maintain a slow reaction rate and reduce the sudden release of heat during neutralization. Controlled release of the SHpho-MFS capable of the ordered production of protons on demand is also achieved because the release “on and off” behavior of protons is repeatedly observed for every cycle.

Environmentally friendly superhydrophilic and superhydrophobic sponges were synthesized using a one-step approach for oil/water separation. A superhydrophilic or superhydrophobic sponge (MFS/CC-DKGM or MFS/CC-PDMS) was synthesized by one-step coating of melamine formaldehyde sponge (MFS) with a mixture of calcium carbonate (CC) rods and deacetylized Konjac glucomannan (DKGM) [or polydimethylsiloxane (PDMS)]. The MFS/CC-PDMS showed excellent absorption capacity, which reached 52–76 g/g following immersion into various types of oil/water mixtures. Furthermore, the MFS/CC-DKGM and MFS/CC-PDMS exhibited excellent water- and oil-flux performances, which reached 4,702 L/m2 h and 19,591 L/m2 h, respectively, when they were used as filters. The MFS/CC-DKGM and MFS/CC-PDMS maintained their wettability characteristics relatively well after the chemical, thermal, and mechanical stability tests.

A lottery draw machine-inspired novel movable air filter (MAF) system is presented in which MAFs are vigorously moved or rotated to generate a high electric field and capture particulate matter (PM) particles. The MAF system purified 500 mL of a hazardous level of PM particles (2016 μg m−3 PM10 and 1040 μg m−3 PM2.5) at a high flow rate of 2.5 m s−1 with high removal efficiencies (99.7% and 98.8% for PM10 and PM2.5, respectively) in 1 min. The MAF system also had a small pressure drop of 3–6 Pa, which was approximately an order or orders of magnitude lower than previously reported values, even at a high flow rate of an order of magnitude higher than previously reported values. The MAF system exhibited excellent recyclability of up to 300 cycles with high removal efficiencies (99.7–98% and 98.8–96.2% for PM10 and PM2.5, respectively). Furthermore, the MAF system could effectively remove 500 mL of PM particles at extremely high concentrations (over 10 000 μg m−3 PM10 and over 3000 μg m−3 PM2.5) with very high efficiencies (over 99.8% and 99.6%, respectively) and a very low pressure drop (6 Pa), and these properties led to the conversion to clean ambient air (24 μg m−3 PM10 and 12 μg m−3 PM2.5) in 15 min.

A simple simultaneous complementary oil-water separation and water desalination system is designed using grafted glass fiber (GF) membranes. Non-fluorinated trialkoxysilanes are grafted to form superhydrophobic and superhydrophilic GF membranes, respectively. Zwitterion sulfobetaine was also synthesized and grafted on the glass fiber to make a superhydrophilic glass fiber membrane. The superwetting grafted GF membranes which are superhydrophobic had a water contact angle of 152° and high separation efficiency (>99%) for ten cycles and the superhydrophilic had an underwater oil contact angle of 156° and high separation efficiency (>98%) for ten cycles. The zwitterionic glass fiber membrane also exhibits excellent removal performance for heavy metal ions and nitrate ions from the water layer. This method is simple and scalable, and provides a versatile way for designing devices that achieve both oil/water separation and water desalination simultaneously.

An alkali-treated Mg–Al layered double hydroxide (A-LDH) is prepared by NaOH treatment of normal Mg–Al LDH (N-LDH) at high temperature. Four NaOH treatments are performed with N-LDH to control the basicity of the LDHs. Among the four A-LDHs, the A-LDH possessing a certain basicity shows several unique characteristics that are not observed in N-LDH. The A-LDH induces a controlled oxidative polymerization of dopamine into spherical polydopamine (Pdop) particles and can effectively oxidize metals (Cu and Al) and nanocarbons (carbon nanotubes (CNTs) and graphite) to produce oxidized CNTs and oxidized/exfoliated graphene oxide with excellent dispersibility. These interesting phenomena are tested by simply mixing the compounds with A-LDH at room temperature without an energy-consuming process and toxic chemicals. Furthermore, A-LDH exhibits excellent catalytic performances for the degradation of organic pollutants such as various azo dyes.

An anti-overturn Janus sponge (AJS) that partially floats/is partially submerged on/under water was prepared. The Janus characteristics originate from the cooperative effect of the hydrophilic part absorbing water and the hydrophobic part generating buoyancy. The AJS with an appropriate hydrophilic/hydrophobic ratio showed excellent floating stability under high waves and strong winds. The AJS also exhibited high adsorption of aqueous pollutants during fast oil/water separation due to its Janus characteristics, stably remained at the oil/water and water/oil interfaces in three liquid multiphases and removed aqueous pollutants at each interface. Because of its great control over the alteration of the ratio, structure, and shape of its hydrophilic and hydrophobic parts, the AJS can be transformed into various types of structures on demand. A pant-like structure that was divided into two branches could successively separate three liquid multiphases (light oil/water/heavy oil) and quickly purify contaminated water during the separation.

Herein, Mg/Fe layered double hydroxide (MF-LDH) hollow nanospheres were successfully prepared by a one-step thermal method. After the thermal treatment of MF-LDH nanospheres at 400 °C, the MF-LDH was converted into the corresponding oxide, Mg/Fe layered double oxide (MF-LDO), which maintained the hollow nanosphere structure. The MF-LDO hollow nanospheres exhibited excellent adsorption efficiency for both As(V) and Cr(VI), showing 99% removal within 5 min and providing maximum removal capacities of 178.6 mg g−1 [As(VI)] and 148.7 mg g−1 [Cr(VI)]. Moreover, it met the maximum contaminant level requirements recommended by World Health Organization (WHO); 10 ppm for As(V) and 50 ppm for Cr(VI) in 10 and 20 min, respectively. Furthermore, Au nanoparticles were successfully introduced in the MF-LDO hollow nanospheres, and the products showed a conversion rate of 100% for the reduction of 4-nitrophenol into 4-aminophenol within 5 min. It is believed that these excellent and versatile abilities integrated with a facile synthetic strategy will facilitate the practical application of this material in cost-effective wastewater purification.

Three types of surface treatments, namely, polyethyleneimine (PEI) coating, short PEI (S-PEI) grafting, and long PEI (L-PEI) grafting, were performed on polydopamine (Pdop)-based catalysts to enhance their catalytic activity and stability. Brush-grafted catalysts were prepared by the stepwise synthesis of Au and short (or long) PEI brushes on Pdop particles (PdopP/Au/S- or L-PEI grafting). PEI-coated Pdop-based catalysts (PdopP/Au/PEI coating) were also prepared as non-brush-grafted catalysts. Among the surface-treated PdopP/Au catalysts, the brush-grafted catalysts (S-PEI and L-PEI grafting) exhibited excellent and stable catalytic performance because the brush grafting enabled the protection of the catalysts against harsh conditions, effective transfer of reactants to the catalysts, and confinement of reactants around the catalysts. The brush-grafted catalysts could also more effectively decompose larger dyes than the non-brush-grafted catalysts. The process-to-effectiveness of PEI coating is the best because the release of Pdop from PdopP/Au was moderately inhibited by the presence of only one layer of PEI coating on the PdopP/Au. Thus, this approach could be an alternative method to enhance the stability of PdopP/Au catalysts.

Magnetic amphiprotic catalysts (MACs) were synthesized by coating magnetic nanoparticles (MNPs) stepwise with polydopamine (Pdop), a polyethyleneimine (PEI) brush, octadecylamine (ODA), and Au. The amphiprotic characteristics of the MACs were tuned by varying the portions of the hydrophilic and hydrophobic moieties. The MACs normally dispersed in the hydrophobic layer but were forced into water to catalytically decompose aqueous pollutants upon the application of a magnetic field. When the magnetic field was turned off, the MACs naturally returned to the hydrophobic layer and catalytically decomposed non-aqueous pollutants. Next, the purified oil was readily separated from the oil/water mixture by using the magnetic field because the MACs absorbed oil. Oil-in-water and water-in-oil wastewater emulsions containing aqueous and non-aqueous pollutants, respectively, were also purified and separated into pure oil and water. A series of wastewater purification steps, including oil/water separation and the decomposition of aqueous and non-aqueous pollutants in both phases, was performed by in situ and continuous processes using the MACs. The MACs also performed catalytic organic reactions in organic solvents.

A convection heat treatment that can replace existing chemical oxidation methods was developed for the preparation of hierarchically oxidized Cu meshes with various surface morphologies, representing a very simple and green route that does not involve toxic chemicals. Three types of Cu meshes [bumpy-like (BL) and short and long needle-like (NL) structures] exhibited similar separation efficiencies of 95–99% over 20 separation cycles, as indicated by their similar water contact angles (WCAs; 147–150°). However, these Cu meshes exhibited different flux behaviors. Excessively rough and excessively smooth surfaces of the Cu mesh resulted in increased resistance to flow and to a decrease of the penetration of oil. A surface with intermediate smoothness, such as the BL-Cu mesh, was necessary for high flux over a broad range of oil viscosities. Furthermore, a less rough surface was more suitable for the separation of highly viscous oil. Computational fluid dynamics (CFD) simulations were carried out to support our experimental results. The BL-Cu meshes also showed outstanding mechanical stability because of their low resistance to the flow of fluids.

A carbonate-based mesoporous magnetic adsorbent IO@CaCO3 was synthesized via a hydrothermal method. The IO@CaCO3 adsorbent removed both anionic (As(V) and Cr(VI)) and cationic (Pb(II)) heavy metal ions at a rate orders of magnitude faster than any conventional adsorbents reported to date; due to synergistic effect of needle-like IO and CaCO3, it completely removed (99.99%) the toxic heavy metal ions from wastewater in only 9 min. In addition, it exhibited excellent As(V), Cr(VI), and Pb(II) removal capacities of 184.1, 251.6, and 1041.9 mg g−1, respectively, over a wide pH range. The heavy metal ion adsorption mechanism involves ion-exchange reactions between the cationic/anionic heavy metal ions and the positively/negatively charged groups on the adsorbent. Along with the batch adsorption tests, heavy metal ion removal by IO@CaCO3 was also performed by column filtration, demonstrating the potential of IO@CaCO3 for use in practical applications. Moreover, the excellent removal efficiencies of the adsorbent for the heavy metal ions up to drinking water level and its easy separation by an external magnetic field enabled it to be effectively reused.

Polydopamine (Pdop) is coated on copper mesh (Cu mesh/Pdop). Upon heat treatment of the Cu mesh/Pdop, Pdop particles are newly formed at the surface of the Cu mesh/Pdop, which is used as a superhydrophilic mesh. After octadecylamine (ODA) is coated on the heat-treated Cu mesh/Pdop, hierarchical and strong ODA crystals are formed by special interactions between the ODA and the Pdop. The surface morphologies of the ODA crystals are tuned by varying the amount of Pdop particles. Similar results are obtained when the sponge is used as a template in lieu of the Cu mesh, and this sponge is used as a superhydrophobic sponge. A self-floating all-in-one device that simultaneously coexists in water as well as in oil is also prepared by combining the Pdop particle-mediated superhydrophilic mesh and superhydrophobic sponge composites. The self-floating all-in-one device simultaneously exhibits excellent removal performance for heavy metal ions in the water layer and excellent separation efficiency of oil in the oil layer due to its amphiprotic nature.

We present the synthesis of polydopamine particle-gold composites (PdopP-Au) and unique release of Au@Pdop core@shell nanoparticles (NPs) from the PdopP-Au upon external stimuli. The PdopP-Au was prepared by controlled synthesis of AuNPs on the Pdop particles. Upon near infrared (NIR) irradiation or NaBH4 treatment on the PdopP-Au, the synthesized AuNPs within the PdopPs could be burst-released as a form of Au@Pdop NPs. The PdopP-Au composite showed outstanding photothermal conversion ability under NIR irradiation due to the ultrahigh loading of the AuNPs within the PdopPs, leading to a remote-controlled explosion of the PdopP-Au and rapid formation of numerous Au@Pdop NPs. The release of the Au@Pdop NPs could be instantly stopped or re-started by off or reboot of NIR, respectively. The structure of the released Au@Pdop NPs is suitable for a catalyst or adsorbent, thus we demonstrated that the PdopP-Au composite exhibited excellent and sustained performances for environmental remediation due to its capability of the continuous production of fresh catalysts or adsorbents during the reuse.

Micropothole-based oxidized (MPO) Cu meshes with various surface morphologies, such as needle-like (NL), hair-like (HL), arch-like (AL), and pine needle-like (PNL) structures, were prepared by controlling the pH and temperature of the oxidation reaction solution. The separation efficiencies of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFTOS)-coated MPO-Cu meshes were found to be 96–99% for oil/water separation, and the meshes maintained this performance over 20 separation cycles without deterioration. The HL mesh with long and flexible structures was outstanding for the separation of low viscosity oils, while the NL mesh with short and rigid structures was optimal for the separation of highly viscous oils. Double-layered meshes consisting of photocatalytic and superhydrophobic meshes exhibited high catalytic performance after the oil/water separation, demonstrating purification of an aqueous pollutant separated from the oil/water mixture.

A facile approach for synthesizing superhydrophobic hollow silica micelles (SHSMs) with hydrophilic cores and amphiprotic (superhydrophobic/hydrophilic) shell structures that act as “all-in-one” smart nanomaterials is presented. The particles possess hydrophilic cores consisting of silica and a polyelectrolyte (PE) network and an amphiprotic shell consisting of superhydrophobic long-chained hydrocarbons and hydrophilic PEs. Due to the unique hydrophilic cores and amphiprotic shells, the particles exhibit extraordinary performance in terms of amphiprotic catalytic reactions in organic and aqueous solutions, oil/water separation and pollutant purification, and an ultrahigh loading capacity of enzymes with significant stability and efficient recyclability. The amphiprotic functionalities of the SHSMs have the potential to allow for a rich range of applications to be explored.

Nanocomposites comprised of magnesium hydroxide (Mg(OH)2) and graphene oxide (GO) were prepared by the controlled precipitation of a magnesium salt on the GO surface. The population of Mg(OH)2 nanocrystals on the GO surface could be varied by varying the Mg(OH)2 precursor amount; the surface area of the resulting Mg(OH)2/GO nanocomposites varied from 75.2 m2 g−1 to 465 m2 g−1. The Mg(OH)2/GO nanocomposite with a surface area of 465 m2 g−1 showed the best performance. Owing to the synergistic effect of the nanoplate structure of Mg(OH)2 and the 2D structure of GO, the obtained Mg(OH)2/GO nanocomposites exhibited high performance in methylene blue adsorption (adsorption capacity: 779.4 mg g−1).

In this paper, we report the preparation of mesoporous silica nanoparticles (MSNPs) using the mobility differences of sulfonate or sulfate-containing materials as etchants. The MSNPs were synthesised by treating silica nanoparticles (SNPs) with styrene sulfonate (SS) or sodium dodecyl sulfate (SDS) under heat. The simple treatment of the SNPs with SS or SDS led to surface etching of the SNPs, resulting in surface roughening and pore generation within the silica structure. The surface structuring of the SNPs could also be controlled by varying the concentration of counter ions of the etchants. This one-step process is very simple, facile, and scalable. The MSNPs appeared almost transparent in an aqueous solution due to their unique surface morphology. The resulting MSNPs also exhibited excellent adsorption and desorption properties for toxic organic pollutants.

We have developed a facile method for the poly(allylamine hydrochloride) (PAH)-assisted synthesis of mesoporous calcium silicate hydrates (PAH-CS) with a large specific surface area (BET = 348.4 m2 g−1) and pore volume (Vp = 1.42 cm3 g−1). Tetraethyl orthosilicate (TEOS) was employed as a silicon source, which was rapidly hydrolyzed and reacted with the amine groups of PAH to form spherical SiO2 nanoparticles (PAH-Si). Subsequently, Ca2+ ions reacted with the silicate anions produced during the dissolution of SiO2 in basic media, leading to the formation of the highly porous 3D networks of PAH-CS that were synthesized only under optimized reaction conditions. The PAH-CS containing an excess of Ca2+ and NH3+ enriched the surfaces with a very high cationic charge (ζ = +65.66 mV)and resulted in an extremely high loading capacity for anionic drugs and proteins. Ibuprofen (IBU) and FITC-labeled bovine albumin (FITC-Albumin) were chosen as a model drug and model protein, respectively, to test the loading and delivery efficiencies of the PAH-CS carriers. The ultrahigh drug loading capacities (DLC) and their release patterns were investigated under controlled pH conditions. Strikingly, the highest DLC reported to date (IBU or FITC-Albumin/carrier (3.35 g or 1 g g−1) was achieved in this work. The PAH-CS had no cytotoxic effect on osteoblast-like MC3T3-E1 cell lines evaluated by the LDH (Lactate dehydrogenase) assay in supernatant medium. Furthermore, the PAH-CS carriers could be entirely transformed to hydroxyapatite after releasing the drug in simulated body fluid (SBF), indicating good bioactivity and biodegradability of the PAH-CS carriers.

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.

AgBr nanostructures with unified shapes and sizes were prepared using simple polyelectrolyte (PE) coatings on various AgBr microstructures that were prepared by mixing silver precursors with hexadecyltrimethylammonium bromide (CTAB) under controlled conditions. The AgBr microstructures (plates, rods, and wires), regardless of initial structures or sizes, transformed into cubic AgBr nanoparticles (CNPs) after only three PE coatings. The electrostatic interactions between the PEs and the CTAB in the AgBr microstructures are the crucial factors that control the shapes and sizes of the AgBr microstructures. During the PE coating, the AgBr microstructures were transformed and rearranged into AgBr CNPs with favorable catalytic faces that enhanced the photocatalytic activity. The size- and shape-controlled AgBr CNPs showed excellent photocatalytic performance for the degradation of methylene orange (MO) dyes under visible-light irradiation without deterioration even after multiple uses.

We report a simple protocol for the fabrication of multiwalled carbon nanotubes (MWCNTs) with a neuron-like structure for loading ultra-high densities of metal nanoparticles (NPs). The MWCNTs were initially coated with an anionic polyelectrolyte (PE), polystyrene sodium sulfonate (PSS), using a noncovalent interaction (CNT/PSS). The neuron-like structures were fabricated through the stepwise assembly of both the positively charged poly(allylamine) hydrochloride (PAH) and negatively charged poly(acrylic acid) (PAA) in a nonstoichiometric ratio on the CNT/PSS as a template. After three coatings with the PEs, the obtained neuron-shaped CNTs were used as a support for loading a high density of multi-metallic NPs. Moreover, a unique characteristic, tunable and side specific growth of the metal NPs, was also observed. Our neuron-like structures with high loadings of multi-metallic NPs were demonstrated to be catalytic materials for the conversion of 4-nitrophenol to 4-aminophenol and as convenient surface-enhanced Raman scattering substrates for biological tags and molecular detection.

A protocol for the synthesis of rattle-type core@shell particles containing Ag@AgCl or Au/Ag@AgCl core structures was developed, and the use of these particles as catalysts for the decomposition of toxic materials was demonstrated. A monometallic Ag or bimetallic Au/Ag core was incorporated into the interior of SiO2 capsules via controlled heat treatment of metal nanoparticle/SiO2-coated polymer particles, resulting in the formation of rattle-type core@shell structures. By appropriate treatments, it was possible to transform the Ag or Au/Ag core into multilevel cores (Ag@AgCl or Au/Ag@AgCl) within the SiO2 capsules (Ag@AgCl@SiO2 or Au/Ag@AgCl@SiO2). This method for the synthesis of rattle-type core@shell particles is useful for further introducing AgCl fused with plasmonic materials into the capsule structures. The rattle-type core@shell structures were used as photocatalysts for the decomposition of organic pollutants such as methyl orange. Furthermore, these nanocatalysts containing semiconductors such as AgCl were also applied toward the reduction of nitrophenol (NPh) to aminophenol (APh). The Ag@AgCl@SiO2 or Au/Ag@AgCl@SiO2 catalysts showed excellent catalytic properties in the decomposition of toxic substances in terms of their activity and reusability.

Our study proposes a novel strategy for the synthesis of Ag derivatives (AgX@Ag (X = Cl and Br) or Ag nano/microtubes) using the controlled chemical reduction or electron-beam irradiation of AgX nanowires (NWs), which are formed from the controlled dewetting of a AgX thin film on colloidal particles. The size of the AgX@Ag and Ag nano/microtubes can be controlled using the AgCl NWs as templates and varying the concentration of NaX. By controlling the concentration of NaBr, heterojunction-structured AgCl/AgBr NWs (H-AgCl/AgBr NWs) can be produced from the AgCl NWs due to a partial ion-exchange reaction (low concentration), and the AgBr NWs produced after a complete ion-exchange reaction between Cl- and Br- are further grown into micrometer-sized AgBr wires (high concentration). The resulting AgX NWs can be transformed into corresponding AgX@Ag or Ag nano/microtubes via a controlled chemical or physical method. The AgX derivatives (AgX@Ag nanotubes (NTs) and AgX NWs) are tested as visible-light-induced photocatalysts for decomposition of methyl orange. The AgX@Ag NTs exhibit the best photocatalytic activities due to the advantages of the core@shell structure, allowing multiple reflections of visible light within the interior cavity, providing a well-defined and clean Ag/AgX interface, and preventing direct adsorption of pollutants on AgX because of the shell structure. These advantages allow AgX@Ag NTs to maintain high catalytic performance even after multiple uses. The approach can also be used as a direct method for preparing Ag nano/microtubes with a tailored size and as a new method for incorporating a AgX NW core into a Ag nano/microtube shell. Our approach is useful for synthesizing various types of one-dimensional heterostructured NWs or metal NTs with controlled structures and properties.

We report a simple synthetic method and the unique properties of four types of individual NPs that are well-dispersed in polyelectrolyte complexes (PECs) from the core to the shell without the formation of alloy or core–shell NPs. Additionally, this result cannot be achieved by conventional methods. By mixing and heating PEs with metal precursors, individual metal NPs stabilized by PEs were synthesized. The four types of individual metal NP-containing PECs were prepared by mixing anionic and cationic PEs involving individual metal NPs. The individual metal NPs were homogeneously distributed within the polymer particles, and their contents were easily tuned by varying the loading fractions of the individual metal NP-containing PEs. The as-obtained PEC–Au/Pt/Ag/Pd (separate entities) exhibited promising performance for surface enhanced Raman scattering (SERS) and catalytic activities, which was further enhanced when the four types of metals demonstrated different optimal composition in comparison to the mixed types, such as the alloy or core–shell NPs. Our results also show that it is necessary to tune the types or individual metal contents of the multi-metallic complexes (individual, alloy, or core–shell) for the control or application of certain properties.

The mixing of Ag ion-doped poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.

We report the theory and synthesis of sub-nanosized gold clusters on reduced graphene oxide (r-GOs). The Au sub-nanoclusters were found to be nucleated and grown at defects of the r-GOs, particularly on nitrogen-induced defects from density functional theory investigation. The resulting Au/r-GOs exhibit an improvement of bulk electrical conductivities and a reduced ratio of the intensity of the D band to that of the G band (ID/IG), compared to the r-GOs without Au nanoclusters. The unique decrease of the ID/IG was demonstrated to be related to the filling of subnano-sized Au clusters on the r-GOs, presumably owing to enhancing the flat geometry of the graphene nanosheets.

A one-step, template-free synthetic method for preparing polymeric microcapsules with iron oxide (γ-Fe2O3) magnetic nanoparticles (MPs) embedded in the polymer shell is reported. Using a simple emulsification of the multiphase mixture containing liquid prepolymer and MPs in chloroform solution, double emulsions comprising a chloroform core and MPs/polymer shell were spontaneously formed. After exposure to UV light, these double emulsions converted to microcapsules with a polymerized composite shell. The evolution from the double emulsions to the microcapsules was examined by confocal laser scanning microscopy. One unusual feature of these microcapsules is the ability to change shape reversibly by osmotic swelling of the water core upon repetitive drying and hydration. The microcapsules had an intrinsic superparamagnetic response due to the presence of the magnetic nanoparticles and could be moved and collected by external magnetic fields.

Our study demonstrates a facile approach for the synthesis of metal NP-embedded freestanding polyelectrolyte complexes (PECs) without sacrificial templates, which can be used as nanoactuators, nanoshutters, and nanofilters. The metal NP-PECs were prepared by mixing metal precursor-preadsorbed cation and anion PEs, using a nonstoichiometric ratio, followed by a controlled heat treatment. The metal NP-PECs showed reversible structural changes such as shrinking or swelling when they were exposed to various pH conditions. During the changes, they were also able to reversibly control the interparticle distance of the metal NPs embedded in the PECs, which has allowed the easy tuning of their catalytic and optical properties. By the reversible control of structural changes, the PECs can also be used as nanoshutters to reversibly control the flow of nanomaterials in the channels or pores. Furthermore, metal NP-embedded PECs, Au/Ag-PECs, were demonstrated to be useful as nanofilters for removing or transforming unwanted materials.

A novel strategy for preventing aggregation, increasing surface area, and maintaining catalytic activity of water-soluble graphene nanosheet (GNS) catalysts is introduced, and use of the synthesized nanocatalyst [GNS (matrix)/metal (catalyst)/metal oxide (spacer)/ceramic (protector)] as recyclable nanocatalysts without loss of performance is demonstrated. Our graphene nanocomposite (GNC) armed with nanoneedles is fabricated by the synthesis of Au on GNS, followed by stepwise synthesis of needle-like IO and SiO2, in order. The distinctive structures of the needle-like layers prevent aggregation and contamination of the GNS catalysts, and allow recycling, both of which enhanced catalytic ability. The research demonstrates the possibility of a safe coating for water-soluble GNS catalysts, which are reactive to ionic species, and their application as nanocatalysts for the chemo-selective transformation of toxic substances. Our sandwich-like GNCs for recyclable nanocatalysts provide a new design concept for reusable GNS catalysts.

A novel protocol for the synthesis of core@shell particles with transformable core structures has been introduced, and its use as a chemical reactor for hierarchical nanomaterials with tunable properties has been demonstrated. A metal, metal/polymer, or bimetallic hollow structure was incorporated into the interior of silica capsules via controlled heat treatment of the inorganic-coated polymer particles. A micrometer-sized capsule was used as a reaction chamber to contain and sustain heat, and metal NPs were used as a controller for the transformation of polymer cores. By varying the thermal conductivities of the metal NPs, it was also possible to confer synthesis of hatlike, UFO-like, or bimetallic hollow structures within the capsule. This novel method for core@shell particles is useful for synthesizing nanomaterials with controlled structures and properties. Furthermore, Pt/Au capsule@SiO2 and Au/polymer@SiO2 showed excellent catalytic properties for the transformation of nitrophenol to aminophenol. This approach could be used to tune the structures and properties of various kinds of polymer matrices.

A facile approach to the development of multifunctional freestanding films consisting of polyelectrolytes (PEs) and polyelectrolyte complexes (nPECs) with highly embedded metal nanoparticles (NPs) was demonstrated. The composite films (nPEC/PE) containing NPs exhibited controllable properties that can be exploited by varying the type and content of NPs with high loading density. The approach described here enables the facile fabrication of conducting and transparent freestanding films with tunable optical/electrical properties, color, and large lateral dimensions with minimal effort in terms of the number of layers and ease of operation.

We report the synthesis ofgraphenes with tunable properties dueto the growth of needlelike iron oxide(IO) nanoparticles on their surfaces.The electrical conductivity, flexibility,and magnetic properties of graphenenanosheets (GNSs) could be tuned ondemand by fine controlling both thesurface coverage and the length of theIO nanoneedles. The degree of cover-age of the IO nanoparticles on the sur-face of the GNSs made it possible to control the resulting properties of theIO/GNSs on demand. As examples oftheir utility, paperlike materials weregenerated by simple filtration, and theresulting IO/GNS nanocompositesshowed extraordinary removal capacityand fast adsorption rates for AsVand CrVIions in water. Another possibleapplication is the preparation of multi-functional films equipped with conduc-tivity, flexibility, and magnetic proper-ties. The fabrication process is easy toscale up at a low cost. In addition, boththe colloidal solution and film forms ofthe resulting IO/GNSs were effectivefor removal of heavy metal ions, mean-ing this material could be utilized foractual industrial applications.

The production of unfunctionalized and nonoxidized graphene by exfoliation of graphite in a volatile solvent, 1-propanol, is reported. A stable homogeneous dispersion of graphene was obtained by mild sonication of graphite powder and subsequent centrifugation. The presence of a graphene monolayer was observed by atomic force microscopy and transmission electron microscopy. The solvent, 1-propanol, from the deposited dispersion was simply and quickly removed by air drying at room temperature, without the help of high temperature annealing or vacuum drying, which shortens production time and does not leave any residue of the solvent in the graphene sheets.

In the present study, a versatile layer-by-layer technique using polyelectrolyte multilayers (PEMs) was used to prepare microcapsules with walls containing photoacid generators (PAGs), which made them optically addressable. By exposure to UV light with a wavelength of 254 nm, the PAGs within the capsule walls were activated, which caused the release of protons from the capsules. This release of protons caused a decrease in the pH of the capsule solution, which then triggered a swelling of the microcapsules. The resulting microcapsules could be opened and closed via alternate repetition of exposure to UV light and washing with neutral water. Prolonged exposure led to a breakage of the capsules, which promoted a rapid release of the entrapped substances.

We report a feasible fabrication of binary complex particles based on polyelectrolyte multilayer-coated particles (PEMPs). Binary complex particles were synthesized by combination of large organic and small inorganic nanoparticles. The PEMPs were prepared by alternating adsorption of two kinds of polyelectrolytes with opposite charges onto colloidal particles. In this structure, polyelectrolytes act as a matrix to bind precursor for metal nanoparticles. Following reduction and hydrolysis of the PEMPs could generate bimetallic complexes onto PEMPs. We found that size and composition of the bimetallic complexes depend on the amount of gold precursor added to the suspension of the PEMPs.

The encapsulation of carbon nanotubes (CNTs) to form a reconfigurable conglomerate within iron oxide microcapsules is demonstrated. The individual CNTs conglomerate and form a core inside the capsule upon exposure to high temperature, while they scatter when subjected to mild sonication at low pH. The assembly/disassembly of CNTs within the capsule was reversible and could be repeated by alternate heating and sonication. Also, the fabrication protocol could be used for the generation of various multifunctional hollow structures. To test the feasibility of using the capsules in real applications, the capacity of the capsules as a heavy metal ion remover was explored. The resulting capsules showed an excellent ability to remove lead and chromium ions. In addition, desorption of the metal ions adsorbed on the CNTs could be induced by exposure to low pH. Thus, encapsulated CNTs might be a recyclable, environmentally friendly agent for the removal of heavy metal ions.

The present study investigated the effects of ionic surfactants on polyelectrolyte multilayer (PEM) films, consisting of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), prepared using a sequential layer-by-layer (LbL) technique. The electrostatic interaction between sodium dodecyl sulfate (SDS) and the PEMs resulted in desorption of the polyelectrolytes from the PEM films, and consequently the thickness of the PEM films was altered, as confirmed by UV−vis, XPS, and AFM studies. Two critical features of this phenomenon include the porous morphology of the SDS-treated films and the simultaneous increase in the thickness of the film. Furthermore, both the rate and amount of polyelectrolytes desorbed from the PEM films could be controlled by varying the surfactant, the outermost layer, and the reaction time. The surface morphology and thickness of the PEM films could be retuned even after formation of PEMs. Thus, controlled desorption of PEs could be an effective tool for the renewal of the structures and properties of PEMs.

We report high-performance top-gated organic field-effect transistors (OFETs) with regio-regular poly(3-hexylthiophene) (rr-P3HT). The high charge carrier mobility in rr-P3HT FETs (0.4 cm2/Vs) was achieved due to the relatively low contact resistance and high crystallinity of rr-P3HT films. The contact resistance was controlled mainly through the use of high work-function platinum (Pt) (5.6 eV) for the charge injection electrode and a top-gate, bottom-contact geometry that enabled an enhanced current injection via current crowding in the staggered device structure. Moreover, the top-gate configuration provided improved device stability in air ambient conditions via the presence of a gate dielectric and gate electrode on top of the organic semiconductor.

Polyelectrolyte brushes loaded with magnetic nanoparticles can be formed through the reaction of immobilized Fe2+/3+ ions in the brush. These particles show very unusual magnetic properties, not normally associated with such small nanoparticles. Upon application of an external magnetic field, the brushes showed reversible dimensional changes.

Polyelectrolyte multilayer films composed of a polycation (poly(allylamine hydrochloride) PAH) and a polyanion (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) PEDOT:PSS) were prepared by a spin self-assembly method, and their electrochemical and electrochromic properties were investigated. The change in the surface charge and the optical absorption spectra of the multilayer films revealed that sequential deposition of polyelectrolyte was successfully achieved during the spin self-assembly. The electrochromic properties of 20-bilayered PAH/PEDOT:PSS were also investigated. The response time for the coloring and bleaching processes was 6.2 and 2.5 s, respectively, and the coloration efficiency was 199.3 cm2/C. These results indicate that a spin self-assembly process could be a viable alternative for the fabrication of electrochromic devices.

The versatile preparation of the polyelectrolyte multilayered capsules functionalized with gold nanorods (AuNRs) is described. By seed-mediated growth of AuNR directly onto the capsules, stable complexation of the AuNRs onto the capsules can be achieved (see image). The resulting capsules show improved optical stability over free AuNRs, as well as tunable optical property depending on aspect ratio of the AuNRs.

Core-in-shell particles with controllable core size have been fabricated from core−shell particles by means of the controlled core-dissolution method. These cores in inorganic shells were employed as scaffolds for the synthesis of metal nanoparticles. After dissolution of the cores, metal nanoparticles embedded in cores were encapsulated into the interior of shell, without any damage or change. This article describes a very simple method for deriving core-in-shell particles with controllable core size and encapsulation of nanoparticles into the interior of shell.

A facile method for preparing gold nanoparticle (AuNP) films with a high loading density based on the seed-mediated growth of AuNPs on a polyelectrolyte multilayer (PEM) is reported. Use of PEMs as a base layer for gold seed adsorption confers controllability on the loading density of the AuNP film and size of the resulting AuNPs. In addition, the shape of the final AuNPs could be varied by adapting various species of polyelectrolytes. The optical response of the AuNP films is stable, because of the relatively uniform distribution of the AuNPs over a large area. The AuNP film has been used as a substrate for surface-enhanced Raman scattering (SERS), and it shows stable and reproducible enhancement in the range from 105 to 107 depending on the fabrication condition.

The formation of raspberry particles from polyelectrolyte multilayer-modified particles is described. This synthesis represents a new use for polyelectrolyte multilayers as nanoscale-thick reaction vessels for the immobilization and reaction of inorganic reagents. The dissolution of Au nanoparticles inside PEM layers that are capped with a SiO2 layer leads to the hydrolysis and subsequent redeposition of SiO2 nanoparticles. The size of these particles is in the 200 nm range and their loading can be controlled by adding various amounts of Au nanoparticles to the PEMs.

Porous capsules composed of hematite, silica, and hematite–silica composites are prepared by a templated synthesis method. Polyelectrolyte multilayer-coated particles (PEMPs) are used to synthesize goethite nanocrystals and the resulting goethite-nanocrystal-embedded PEMPs (PEMP–goethite) are then used as templates to form porous capsules. The surface morphology and surface area of the porous capsules can be controlled by the size of the PEMP–goethite template, which is determined by the extent of growth of the goethite nanocrystals. By controlling the surface morphology and area, it is also possible to tune the sensitivity of the hematite capsules for use as gas-sensing materials. This surfactant-free approach is also used to synthesize silica and silica-based composite capsules with a controllable porous shell thickness. This straightforward approach can also be extended to the synthesis of other porous capsules or particles with a controllable surface morphology.

A scalable synthesis of core/shell capsules by the heat treatment of polyelectrolyte-multilayer-particle reactors, in which metal nanoparticles are embedded (see figure), is demonstrated. Using this method, it is possible to prepare a wide variety of core/shell structures from a variety of materials, and to control the size, dispersity, and core composition of mono- or bimetallic core particles.

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.

Polyelectrolyte multilayer capsule reactors (PEMCRs) for the synthesis of two types of nanoparticles were prepared. The tunable PEMCRs containing two different functional groups that can be used to synthesize two types of nanoparticles simultaneously and to control the composition of two types of nanoparticles within the shell of PEMCs. These PEMCRs enabled the composition as well as the amount of the loaded two types of nanoparticles within the shell of PEMCs to be controlled by the copolymer ratio and the number of reaction cycles. Another interesting finding is that, as a result of the synthesis of two types of nanoparticles, these specially designed PEMCs containing both silver and goethite nanocrystals can be used as antimicrobial capsules, which can move by an external magnetic field. Such a technology has the potential for use in sterilization at the desirable sites.

Interior decorating: Polymerization of styrene sulfonate monomers on the inner surface of polyelectrolyte hollow capsules results in polymers having molecular weights an order of magnitude higher than those produced in solution. The shape of the capsules after polymerization can be manipulated by varying the styrene sulfonate content (see SEM images; a: 25 wt %, b: 40 wt %).

A new method for fluorescence imaging based on a polymeric photobase generator containing oxime-urethane groups was developed via the use of fluorescamine, a prefluorescent amino-group dye. The fluorescent image obtained is stable and has a high contrast and good resolution (see Figure). In addition, it is possible that the fluorescent image can be erased or restored by the alternative treatment of base and acid.

A photonic crystal structure with a refractive index that gradually changes in the specific direction of the crystal is demonstrated (see Figure). The colloidal photonic crystal was obtained by infiltration of a monomer and organic dopant with a high refractive index into the colloidal opal, followed by interfacial gel polymerization. The resulting colloidal crystal has a gradually varying stop-band at different positions in the crystal when the incident light is normal to the {111} crystallographic axis.

Portable, non-toxic, and user-friendly sponge composites decorated with polyelectrolyte (PE) brushes were developed for the fast and efficient removal of heavy metal ions from waste water or drinking water. The polyacrylamide (PAM) and polyacrylic acid (PAA) brushes were grafted onto the sponge via ⿿grafting-from⿿ polymerization. For the polyethyleneimine (PEI) brush, ⿿grafting-to⿿ polymerization was used. A polydopamine (Pdop) layer was first coated on the sponge. Then, PEI was grafted onto the Pdop-coated sponge via a Michael addition reaction. The PEI-grafted sponge exhibited the best adsorption capacity and the fastest reaction rate of all the brushes due to the numerous adsorption sites of the PEI. The adsorption performance of two different PEI-grafted sponges depended on the molecular weight (MW) of the PEI. Simply by being dipped into a glass of water, non-toxic PEI-grafted sponge instantly removed the low concentration heavy metal ions, demonstrating a practical application for individual users.

Pristine polyelectrolyte multilayers (PEMs) composed of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were treated with an anionic surfactant to prepare rough and porous templates formed by surfactant-induced polyelectrolyte (PE) desorption from pristine film. These templates served as a base substrate for the growth of fresh multilayers using the same polyelectrolyte pair. Growth solutions with or without NaCl salt were used for the formation of fresh multilayers. The growth behavior of fresh multilayers on rugged PEMs was much different than that of a conventional film. The fresh multilayers on templates showed both nonlinear and linear growth behaviors and their surface morphologies differed from those of the rugged template or the pristine film. Unique adsorption behaviors were also observed when PEs were adsorbed onto the templates. UV–Vis spectroscopy and atomic force microscopy (AFM) were employed to study the entire system. These results of the present study offer a unique perspective on the usual model of PEM growth, and provide an alternative route for construction of PEMs with different architectures.

The transition metal copper (II) ion (Cu2+) was effectively coordinated with a single-walled carbon nanotube (SWCNT) to produce a SWCNT–Cu2+ complex by a metal coordination reaction. Since the complex was very reactive towards the carboxylic acid group, the chemical functionalization of SWCNTs was easy to accomplish. This approach was used to functionalize the surface of the SWCNTs with stearic acid or ethylenediaminetetraacetic acid for tuning of the relative hydrophobicity and hydrophilicity of the surface, respectively. The mild reaction conditions used for metal coordination of the SWCNTs minimized the defects that result from chemical modification of SWCNT. Thus, the electrical properties of unmodified SWCNTs were preserved. Various analytical techniques, including Fourier transform infrared spectroscopy, thermal gravimetric analysis, ultraviolet–visible spectroscopy, and water sorption isotherm measurements, were used to characterize the surface properties of the functionalized SWCNTs. Functionalization of SWCNTs by metal coordination reaction effectively modified the SWCNT surface, while conserving the excellent physical properties of the SWCNTs. The surface properties of the SWCNTs were easily tuned by introduction of the functional groups required for specific applications.

An anthracene-containing polymer was applied to a fluorescent image recording material. Irradiation of a copolymer, which was prepared by copolymerization of methyl methacrylate and 9-anthrylmethyl methacrylate, led to disappearance of the flourescence due to the photochemical reaction of anthracene groups. The fluorescence of a copolymer film was disappeared due to the photodimerization reaction of anthracene groups under N2 atmosphere, while under atmospheric conditions, it was disappeared faster rate than under N2 atmosphere due to not only the photodimerization but also the endoperoxide formation reaction of anthracene groups. A clear fluorescent image with the line width of 0.5 um was obtained on a copolymer film through the photochemical reaction of anthracene gropus.