As-prepared Silica Research Articles

PH-Sensitive oligopeptide magnetic mesoporous silica beads for deoxyribonucleic acid extraction.

Exploring novel synthesis strategies for magnetic beads to extract nucleic acids is of great significance in the field of in vitro diagnostics. In the present research, monodisperse magnetic mesoporous silica beads were synthesized via the thermolysis reaction of Fe(acac)3 by using large-pore dendritic silica colloids as templates, and were further functionalized with a highly pH-sensitive histidine-glutamate co-oligopeptide for deoxyribonucleic acid extraction. The large-pore dendritic silica colloid scaffolds were utilized for high-density incorporation of superparamagnetic iron oxide nanoparticles within the vertical channels. The morphology and properties of the as-prepared pH-sensitive oligopeptide magnetic mesoporous silica beads were evaluated by transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometry, X-ray photoelectron spectroscopy, X-ray diffraction testing and so on. The average size of the obtained magnetic beads was 370 nm in diameter with a narrow size distribution. The saturation magnetization and magnetic content of the resultant magnetic beads were 25 emu g-1 and 59%, respectively. Moreover, the magnetic mesoporous silica beads exhibited an obvious pH-responsive behavior. Due to these remarkable features, successful deoxyribonucleic acid capture using the as-prepared pH-sensitive oligopeptide magnetic mesoporous silica beads was achieved.

Preparation of Monodisperse Silica Mesoporous Microspheres with Narrow Pore Size Distribution.

The purpose of this study is to prepare monodisperse silica mesoporous microspheres with narrow pore size distribution to promote their application in the field of liquid chromatography. An improved emulsion method was used to prepare silica mesoporous microspheres, and the rotary evaporation temperature, emulsification speed, dosage of porogen DMF, and dosage of the catalyst NH3·H2O were optimized. Subsequently, these microspheres were respectively treated by alkali-heating, calcination, and sieving. The D50 (particle size at the cumulative particle size distribution percentage of 50%) of as-prepared silica mesoporous microspheres is 26.3 μm, and the D90/D10 (the ratio of particle size at a cumulative particle size distribution percentage of 90% to a cumulative particle size distribution percentage of 10%) is 1.94. The resultant silica mesoporous microspheres have distinctive pore structures, with a pore volume of more than 1.0 cm3/g, an average pore size of 11.35 nm, and a median pore size of 13.4 nm. The silica mesoporous microspheres with a large particle size, uniform particle size distribution, large average pore size and pore volume, and narrow mesopore size distribution can basically meet the requirements of preparative liquid chromatographic columns.

Novel process for high value utilization of high-alumina fly ash: valuable metals recovery and mesoporous silica in situ preparation.

Extraction of valuable metals besides silica from high-alumina fly ash is one of the most important high-value utilization pathways. However, it is difficult to realize high-efficiency extraction due to the stable structure e.g. of quartz and mullite. In this paper, mineral phase transformation for valuable metal recovery and mesoporous silica in situ preparation from fly ash by a selective acid leaching method was proposed. The mineral phase transformation, dissolution behavior of each metal, and pore structure of fly ash derived mesoporous silica were systematically investigated. The results show that the co-activation of fly ash by Na2CO3-K2CO3 formed the phases of kalsilite and (Na, K)AlSiO4. During the acid leaching process, Al, Li, and Ga could be leached with the efficiencies of 86.17%, 89%, and 80% in the FK system. In the FN system, the efficiencies of Al, Li, and Ga are 92.38%, 95%, and 83%, respectively. The crystal plane (002) was destroyed for kaliophilite while all the crystal planes were destroyed for nepheline. With the increase of HCl solution concentration, the porous silica exhibited the same change order of pore shape. The pore structure of as-prepared porous silica was type IV and the hysteresis loop was type H3, and the specific surface areas could be 565.54, 448.02, and 746.76 m2 g-1, respectively. Finally, the leaching liquors can be used to produce crystal aluminum chloride, lithium carbonate and gallium. This paper might provide technical support for full recycling of high-value resources from fly ash.

Enhanced Adsorption of Azoxystrobin from Water by As-Prepared Silica Nanoparticles

Nanoparticles are of great interest for water treatment as they remove a significant portion of water contaminants. In analogy to these emerging practices, the present work investigated the feasibility of using silica nanoparticles (SiO2-NPs) to remove azoxystrobin from an aqueous solution. We investigated the effects of experimental parameters, such as solution temperature, adsorbent dosage, contact time, and initial azoxystrobin concentration, on the removal efficiency of azoxystrobin. Structural and chemical analysis of the synthesized nanoparticles was performing using X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), and surface studies. The percentage of azoxystrobin removal efficiency was 92.8 at an initial azoxystrobin concentration of 10 mg/L. The result showed that by increasing the adsorbent dosage from 0.005 to 0.1 mg, the percentage removal efficiency of azoxystrobin from aqueous solution increased significantly from 59.72% to 95.21%. At the same time, the adsorption amount of azoxystrobin in equilibrium decreased with increasing temperature. It was found that the optimum temperature for removing azoxystrobin was 20 °C. Although the study was conducted under well-controlled laboratory conditions, the silica nanoparticle system showed excellent performance in removing a significant amount of azoxystrobin, making it a potential alternative/cooperator in water treatment for removing pesticides from aqueous solutions.

Antibacterial Mesoporous Silica Granules Containing a Stable N-Halamine Moiety.

High-efficacy and regenerable antimicrobial silica granules were prepared via oxa-Michael addition between poly(vinyl alcohol) (PVA) and methylene-bis-acrylamide (MBA) under the catalysis of sodium carbonate in an aqueous solution. Diluted water glass was added, and the solution pH was adjusted to about 7 to precipitate PVA-MBA modified mesoporous silica (PVA-MBA@SiO2) granules. N-Halamine-grafted silica (PVA-MBA-Cl@SiO2) granules were achieved by adding diluted sodium hypochlorite solution. It was found that a BET surface area of about 380 m2 g-1 for PVA-MBA@SiO2 granules and a Cl+% of about 3.80% for PVA-MBA-Cl@SiO2 granules could be achieved under optimized preparation conditions. Antimicrobial tests showed that the as-prepared antimicrobial silica granules were capable of about a 6-log inactivation of Staphylococcus aureus and Escherichia coli O157:H7 within 10 min of contact. Furthermore, the as-prepared antimicrobial silica granules can be recycled many times due to the excellent regenerability of their N-halamine functional groups and can be saved for a long time. With the above-mentioned advantages, the granules have potential applications in water disinfection.

Structure and near-infrared spectral properties of mesoporous silica for hyperspectral camouflage materials

Mesoporous silica materials were prepared via a hydrothermal method by adjusting the content of trimethylbenzene (TMB) and PEO-PPO-PEO block copolymer (F127) in mesoporous silica. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy(TEM), nitrogen adsorption–desorption analysis(BET),Fourier transform-infrared spectroscopy (FTIR) and Visible near infrared spectrophotometry (VIS-NIR). The effects of mesoporous structure on the water load capacity and near-infrared spectra were systematically then studied. The results showed that the pore size and volume of the mesoporous silica could be tuned by varying the dosage of TMB and F127. In addition, the hygroscopicity of the mesoporous silica was linearly dependent on the pore size and volume, and the as-prepared mesoporous silica had NIR spectral features similar to those of vegetation leaves. More interestingly, as the water content increased, the water absorption peak of the mesoporous silica in the NIR wavebands was closer to that of natural leaves, showing greater similarity. Finally, camouflage coatings were prepared by using the as-prepared mesoporous silica powder as a functional filler and water-borne polyurethane as an adhesive. The cosine similarity between the camouflage coating and natural leaves reached 98.49%, suggesting that the camouflage coating achieved strong similarity in simulating the reflection spectra of plant leaves, potentially providing a new approach to the design of functional fillers of camouflage materials.

A Facile Approach to the Hydrothermal Synthesis of Silica Nanoparticle/Carbon Nanostructure Luminescent Composites.

Luminescent carbon nanostructures (CNSs) have been intensively researched, but there is still no consensus on a fundamental understanding of their structure and properties that limits their potential applications. In this study, we developed a facile approach to the synthesis of luminescent composite SiO2 nanoparticles/CNSs by the targeted formation of a molecular fluorophore, as the significant luminescent component of CNSs, on the surface of a silica matrix during a one-stage hydrothermal synthesis. Silica nanoparticles were synthesized by reverse microemulsion and used as a matrix for luminescent composites. The as-prepared silica nanoparticles had a functional surface, a spherical shape, and a narrow size distribution of about 29 nm. One-stage hydrothermal treatment of citric acid and modified silica nanoparticles made it possible to directly form the luminescent composite. The optical properties of composites could be easily controlled by changing the hydrothermal reaction time and temperature. Thus, we successfully synthesized luminescent composites with an emission maximum of 450 nm, a quantum yield (QY) of 65 ± 4%, and an average size of ~26 nm. The synthesis of fluorophore doped composite, in contrast to CNSs, makes it possible to control the shape, size, and surface functionality of particles and allows for avoiding difficult and time-consuming fractionation steps.

An efficient amine-modified silica aerogel sorbent for CO2 capture enhancement: Facile synthesis, adsorption mechanism and kinetics

At present, how to develop an economical and efficient solid adsorbent for CO2 capture at low temperature still remains a challenge. In this work, amine-modified silica (SiO2) aerogels were achieved by grafting with 3-(Aminopropyl) triethoxysilane (APTES) through a simple ambient pressure drying process, and verified as efficient adsorbents for CO2 capture. The effects of sol pH value and APTES concentration on the microstructure and CO2 adsorption property of as-prepared amine-modified silica aerogels (AMSAs) were investigated in detail. A double exponential model was proposed to reveal the kinetics adsorption mechanism of the AMSAs for the first time. It demonstrated that the as-prepared AMSAs were amorphous with a three-dimensional network structure composed of nanoparticles. And the AMSAs presented a high CO2 adsorption capacity of 3.37 mmol·g−1 at 70 °C. After 10 adsorption-desorption cycles, the AMSAs still kept 87.6% of the original capacity, exhibiting long cycle stability. Moreover, the kinetic adsorption behavior could be well simulated by the double exponential model, and the CO2 diffusion process was the speed-controlling step in the whole CO2 adsorption process. The diffusion active energy of AMSAs on CO2 capture was also calculated. This synthesis method is facile and environmental-friendly, which is of great significance to the large-scale production of SiO2 aerogel, and may provide a novel reference for the preparation of CO2 low-temperature adsorbents with high adsorption performance and good cycle stability.

Mechanically robust anti-fingerprint coating on polycarbonate substrate

Mechanical robustness is required for a wide range of protective coatings for their long-term usage. It is particularly crucial for the coatings on polymeric substrates to maintain the surface free of contamination such as dust and fingerprint. Here, we have developed an effective fabrication method to prepare amphiphobic anti-fingerprint coating on polycarbonate (PC) substrates. Thin films with porous silicon dioxide (SiO2) nanoparticles were deposited via pulse laser deposition on plasma pre-treated PC substrate. After the coating is applied, trichloro(1H,1H,2H,2H-perfluorooctyl) silane (PFTS) was assembled on the silica surface. The as-prepared PFTS-treated silica coating is superhydrophobic with water contact angle at 155.2 ± 1.8° and highly oleophobic with a contact angle of 133.6 ± 3.3° with diiodomethane. The coating also displays excellent adhesion with the PC substrate. The developed room temperature deposition process makes it potentially applicable for other low melting point polymeric substrates towards a wider range of functional surface applications.

Durable self-polishing antifouling coating based on fluorine-containing pyrrolidone amphiphilic copolymer-functionalized nanosilica

Marine biofouling is detrimental to ships and has been a significant issue in the marine industry for several decades. The development of effective, long-term, and environment-friendly antifouling coating is important but remains a challenge in oceanographic engineering. A series of novel amphiphilic block copolymers (PVP-co-PTFEMA), containing hydrophilic segments (N-vinylpyrrolidone, or NVP) and hydrophobic segments (trifluoromethyl methacrylate, or TFEMA), are grafted on the nanosilica surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The as-prepared amphiphilic copolymers-functionalized silica, SiO2-g-(PVP-co-PTFEMA), can be blended well with self-polishing resin, which could obtain a new type of self-polishing nanocomposite coating. The SiO2-g-(PVP-co-PTFEMA) based composite coating exhibits satisfactory antibacterial and antifouling properties due to the synergistic effect of a strong hydration layer of hydrophilic NVP fragments and low adhesion of hydrophobic TFEMA unit. The slow hydrolysis of the as-prepared self-polishing nanocomposite coating results in the formation of micro/nano structures due to the exposure of SiO2-g-(PVP-co-PTFEMA) in seawater. Moreover, the SiO2-g-(PVP-co-PTFEMA) based nanocomposite coating exhibits high mechanical durability. The as-prepared self-polishing nanocomposite coating combines outstanding antifouling performance and high mechanical durability, which could be an ideal choice in marine antifouling applications.

Anisotropic porous ceramic material with hierarchical architecture for thermal insulation

Porous ceramic materials are attractive candidates for thermal insulation. However, effective ways to develop porous ceramics with high mechanical and thermal insulation performances are still lacking. Herein, an anisotropic porous silica ceramic with hierarchical architecture, i.e. long-range aligned lamellar layers composed of hollow silica spheres, was fabricated applying a facile bidirectional freezing method. Due to such anisotropic structure, the as-prepared porous silica ceramic displays low thermal conductivity across the layers and high compressive strength along the layers. Additionally, the anisotropic porous silica ceramic is fire-resistant. As a proof of concept, a mini-house was roofed with the anisotropic porous silica ceramic, showing that the indoor temperature could be stabilized against environmental temperature change, making this porous ceramic a promising candidate for energy efficient buildings and other industrial applications. Our study highlights the possibility of combining intrinsically exclusive properties in engineering materials through constructing biomimetic porous structures.

Nanostructured Shell-Layer Artificial Antibody with Fluorescence-Tagged Recognition Sites for the Trace Detection of Heavy Metal Ions by Self-Reporting Microsensor Arrays.

Herein, a strategy for a metal ion-imprinted artificial antibody with recognition sites tagged by fluorescein was carried out to construct the selective sites with a sensitive optical response signal to the specific metal ion. The synthesized silica nanoparticles were modified by the derivative residue group of 3-aminopropyltriethoxysilane conjugated with a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) molecule through the hydrolysis and condensation reactions. The as-prepared silica nanoparticles were encapsulated by metal ion (Cu2+, Cd2+, Hg2+, and Pb2+)-imprinted polymers with nanostructured layers through the copolymerization of ethyl glycol dimethyl methacrylate (EGDMA) as a cross-linker, AIBN as an initiator, metal ions as template molecules, AA as a functional monomer, and acetonitrile as a solvent. The layers of molecular imprinted polymers (MIPs) with a core-shell structure removed template molecules by EDTA-2Na to retain the cavities and spatial sizes to match the imprinted metal ions. The microsensor arrays were achieved by the self-assembly technique of SiO2@MIP nanoparticles on the etched silicon wafer with regular dot arrays. The nanostructured-shell layers with fluorescence-tagged recognition sites rebound metal ions by the driving force of concentration difference demonstrates the high selective recognition and sensitive detection to heavy metal ions through the decline of fluorescence intensity. The LOD concentration for four metal ions is down to 10-9 mol·L-1. The method will provide biomimetic synthesis, analyte screen, and detection of highly dangerous materials in the environment for theoretical foundation and technological support.

Influence of Fluorine-Containing Monomer Content on the Hydrophobic and Transparent Properties of Nanohybrid Silica Polyacrylate Coating Materials.

Nanosilica-modified, fluorine-containing polyacrylate hybrid coating materials, consisting of dodecafluoroheptyl methacrylate (DFMA), methyl methacrylate (MMA), 2-ethyl hexyl acrylate (2-EHA), 3-(trimethoxysilyl) propyl methacrylate (KH-570), and tetraethylorthosilicate (TEOS), are synthesized successfully by free radical polymerization and the sol–gel process. It is revealed that the content of the fluorine-containing polyacrylate hybrid coating materials from DFMA monomers significantly improves the properties of the films. The polyacrylate coating film prepared with a weight ratio of DFMA/MMA at 1:5 exhibits the largest water contact angle of 105.4°, which demonstrates that DFMA can effectively improve the hydrophobicity of the coating film. Moreover, the silicon coupling agent (KH-570) is used to graft silica with acrylate. Spherical in shape, the surface morphology of the nanohybrid film exhibits a core–shell structure, which increases the surface roughness and enhances the hydrophobic properties. The as-prepared fluorine-containing nanohybrid silica polyacrylate film possesses a high transmittance of 89–97% in the visible light region, indicating its potential as a very attractive solution in many practical areas.

Spectroscopic and luminescent properties of Nd3+-Al3+ co-doped silica glass prepared by spark plasma sintering

The Nd3+-Al3+ co-doped silica glass has drawn much attention due to the stability and efficient lasing emissions, while the high preparation temperature and residual hydroxyl groups restrict the further improvement of optical performance. In this work, transparent Nd3+-Al3+ co-doped glasses have been synthesized by spark plasma sintering at 980°C within 10 mins. Besides, adopting mesoporous powders as raw materials is beneficial to the homogeneous dispersion of ions in the glass. The transmittance, structure and luminescent properties were systematically investigated. The Judd-Ofelt intensity parameters were obtained to analyze the Al3+ co-doping effects. The PL intensity strongly depends on the ions concentration and the best value is obtained when the Nd3+ concentration is 1.0 mol% and ratio of Nd:Al is 1:7. In addition, the calculated emission cross section is 2.12, which is larger than the majority of previously reported values, suggesting that as-prepared silica glasses are candidates for laser host materials.

Synthesis of Mesoporous Silica Xerogel from Geothermal Sludge using Sulfuric Acid as Gelation Agent

A large amount of sludge is produced by the geothermal brine at the Dieng Geothermal power plant, exceeding 165 tons per month. This sludge is generally not utilized, except for use in landfills. The precipitate (sludge) is primarily composed of silica. The aim of this research is to synthesis mesoporous silica (SiO2) xerogel from geothermal sludge (GS) and to investigate the effects of pH as an effort to elevate the economic value of sludge through alkaline extraction followed by acidification. SiO2 xerogel was prepared by extracting the GS to become sodium silicate (Na2SiO3) assisted by a base NaOH and precipitated using H2SO4 as a gelation agent. The FTIR analysis of the SiO2 xerogel showed a group of silanol (Si-OH) and siloxane (Si-O-Si). The XRD analysis indicated that SiO2 xerogel was amorphous. Furthermore, it was observed from nitrogen absorption-desorption using BET (Breneur-Emmet-Teller) method test that decreased pH tends to the specific surface area increase, and the pore size becomes decrease. The largest specific surface area observed at SiO2 xerogel prepared at pH of 5.5 reached 400.10 m2/g with a pore size of 4.5 nm. The pore sized for all cases was in the range of 4 ~12 nm, indicating that the SiO2 xerogels were mesoporous. Pore size of the as-prepared silica affected the thermal stability property of the sample.

A docosyl-terminated polyamine amphiphile-bonded stationary phase for multimodal separations in liquid chromatography

A convenient synthetic approach to a linear alkyl-polyamine amphiphilic chromatographic selector was proposed. Successive immobilization of the amphiphile onto silica gel afforded a multimodal stationary phase for high-performance liquid chromatography (HPLC). The as-prepared silica material was studied comparatively with a conventional octadecyl (C18) and an amide-embedded C18 stationary phase. The new uniform docosyl-triamine tandem was featured by an enhanced shape selectivity towards geometric isomers, and a low silanol activity towards alkaline solutes. The presence of multiple amino groups rendered the new adsorbent operable in different modes, such as hydrophilic interaction and ion-exchange modes. The satisfactory performance of the said stationary phase in separating different classes of analytes, including polycyclic aromatic hydrocarbons, flavonoids, tricyclic antidepressants, calcium channel blockers, aromatic acids, inorganic anions, nucleosides and estrogens, revealed its great potential and high adaptability for multipurpose LC utility.

Tetrabutylammonium bromide assisted preparation of monodispersed submicrometer silica particles

In this work, we demonstrate a new, facile approach for preparation of monodispersed, submicrometer silica particles via a tetrabutylammonium bromide (TBABr) assisted Stöber method. Sizes of the resulting silica particles increased from 0.39 to 1.08 μm with polydispersity lower than 5 % while the concentration of TBABr in the reaction media was elevated from 0 to 20.0 mM. The presence of TBABr molecules was able to effectively suppress the condensation rate of silanol monomers during the Stöber reaction, which, in turn, slowed the formation of silica seeds and thus accounted for growth of large silica particles. The use of tetraethylammonium bromide (TOABr), a quaternary ammonium agent with longer alkyl chains, instead of TBABr, yielded monodisperse silica particles more hydrophobic in character, making it feasible to tailor the surface properties of the as-prepared silica particles.

High surface N-/O-doped microporous carbons for stable supercapacitor and carbon dioxide sorption applications

Abstract A series of N-/O-doped microporous carbon materials are prepared through the KOH activation of N-doped microporous carbon nanospheres (MCNs) directly prepared from the carbonization of as-prepared mesoporous silica nanospheres (MSNs). Different amounts of KOH are employed to prepare KOH-activated MCNs: MCN–nKOH (where n denotes the weight ratio of KOH to MCN). Compared to nonactivated N-doped MCN, the N-/O-doped MCN–nKOH series reveal superior gas uptake abilities. The MCN–2KOH sorbs 496.8 cm3 g−1 (22.17 mmol g−1) of CO2 at 196 K, 2.12 wt% (10.50 mmol g−1) of H2 at 77 K, and 185.5 cm3 g−1 (8.27 mmol g−1) of CH4 at 196 K. The electrochemical capacitive properties are evaluated by both 3-electrode and 2-electrode measurements. Compared to MCN, the MCN–nKOHs displays enhanced rate capabilities of capacitance. MCN–2KOH shows the highest specific capacitance of 459.6 F g−1 and maximum specific energy of 37.6 Wh kg−1 at 0.1 A g−1. It also exhibits high specific power of 53323 W kg−1 at 120 A g−1. The MCN–nKOH electrodes show superior electrochemical cycling stabilities up to 30000 cycles. The symmetric 2-electrode MCN–2KOH supercapacitor also displays high capacitance of 322.6 F g−1 and energy density of 14.8 Wh kg−1 at 0.1 A g−1.

Fabrication of Microporous Metal-Organic Frameworks in Uninterrupted Mesoporous Tunnels: Hierarchical Structure for Efficient Trypsin Immobilization and Stabilization.

Hierarchically porous metal-organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites.

Fabrication of 3D silica with outstanding organic molecule separation and self-cleaning performance

The existing oil-water separation materials are often limited by their cost, efficiency and environmental implications, so they are difficult to achieve effective utilization in industry. Although silica nanoparticles have excellent environmental-friendly and rich raw materials, their use has been restricted due to poor porous structure or complex preparation process. Herein, we adopt a growth-aggregation-modification-growth strategy to prepare superhydrophobic silica with three-dimensional (3D) structure. Findings show that the as-prepared silica has a 3D network structure of a size of 11 µm, a pore volume of 2.79 cm3/g and an absorption capacity of 2.98 mL/g towards castor oil. Particularly, superhydrophobic silica exhibits an outstanding organic molecule separation performance from series of surfactant stabilized oil-in-water emulsions with size less than 10 µm and dyes in water. In addition, the 3D silica can act as a functional additive in polydimethylsiloxane (PDMS) for enhancing its hydrophobicity. The substrates coated with PDMS/silica composite present outstanding oil/water separation and self-cleaning performance which is due to the silica particles have excellent superhydrophobicity and porous 3D network. In terms of the well available low-cost raw materials and simple preparation method, the superhydrophobic 3D silica could find promising applications in the treatment of oily wastewater or preparation of self-cleaning surfaces.