Water treatment via non-membrane inorganic nanoparticles/cellulose composites

Nanomaterials offer innovations in water purification technology with decreased operational and capital cost, reduced dosage, and improved pollutant selectivity. In particular, inorganic nanoparticles (NPs)/cellulose hybrid nanocomposites have attracted growing interest due to the unique properties of cellulose and high specific surface area of NPs and their pollutant selectivity. The integration with cellulose brings benefits to inorganic NPs for water treatment, including preventing agglomeration, ensuring colloidal stability, and allowing for separation by magnetic nanoparticles after purification. In this review, firstly, conventional water treatment technologies are introduced (Section 1). Following this, an overview of inorganic NPs/cellulose composites for water treatment (Section 2) is presented. Moreover, engineering of such hybrid composites is discussed (Section 3). Furthermore, water purification of inorganic NPs/cellulose through adsorption of pollutants (Section 4) and non-adsorption (catalytic, photocatalytic, and antibacterial) activities (Section 5) are highlighted. Finally, conclusions and outlook are provided (Section 6).     

Synthesis of platinum nanoparticles by aerosol assisted deposition method

An atmospheric pressure aerosol assisted deposition method has been developed to grow highly oriented nanoparticles and thin continuous films of platinum on a variety of substrates for applications such as catalysts including their use in proton exchange membrane fuel cells. Pt nanoparticles with sizes ranging from 4 nm to 78 nm were synthesized on Si, silicon dioxide coated Si substrates and carbon nanotubes. The size and density of the nanoparticles was found to depend strongly on the precursor carrier gas flow rate and deposition time. The particles showed preferential orientation of (111) that was independent of substrate used. The resulting nanoparticles were characterized by Scanning Electron Microscopy, X-ray Diffraction Spectroscopy and X-ray Photoelectron Spectroscopy in order to obtain information about their morphology, crystallinity and composition. The method developed can deposit uniform coatings of highly oriented, pure Pt nanoparticles without the need of any substrate pretreatment such as surface functionalization, deposition of seed layer for electrodeposition on insulating or semiconducting substrates, and without the use of expensive vacuum equipment.     

Synthesis and stabilization of selenium nanoparticles on cellulose nanocrystal

Selenium nanoparticles of 10-20 nm in diameter have been prepared using cellulose nanocrystal (CNXL) as a reducing and structure-directing agent under hydrothermal conditions. Na₂SeO₃ was reduced to form elemental selenium nanoparticles under hydrothermal conditions. During the hydrothermal process (120-160 °C), CNXL rods were mainly maintained and selenium nanoparticles were interfacially bound to the CNXL surface. The reaction temperature affects the sizes of interfacially bound selenium nanoparticles. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and transmission electron microscope (TEM) were employed to characterize interfacially bound selenium nanoparticles on CNXL surface.     

X-ray mirrors on flexible polymer substrates fabricated by atomic layer deposition

Atomic layer deposition (ALD) techniques were used to fabricate W/Al₂O₃ superlattices with high X-ray reflectivity on flexible Kapton® polyimide and polyethylene naphthalate (PEN) polymer substrates. Reflectivities of 78% and 74% at λ = 1.54 Å were measured for 6-bilayer W/Al₂O₃ superlattices on Kapton® polyimide and PEN, respectively. These excellent X-ray reflectivities are attributed to precise bilayer thicknesses and ultrasmooth interfaces obtained by ALD and smoothing of the initial polymer surface by an Al₂O₃ ALD layer. The conformal ALD film growth also produces correlated roughness that enhances the reflectivity. These W/Al₂O₃ superlattices on flexible polymers should be useful for ultralight and adjustable radius of curvature X-ray mirrors.     

Matrix-assisted pulsed laser deposition of polymer and nanoparticle films

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was used to deposit films of Poly(9,9-dioctylfluorene) - PFO and Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3]. The PFO was dissolved in different matrices, like chloroform-CHCl3, tetrahydrofuran - THF and toluene with a 0.5 wt % concentration, while Ge(TPC)OCH3 was diluted in THF with a concentration of 0.01 wt %. The frozen targets were irradiated with a KrF excimer laser. The, films presented good emission properties to be exploited in light emitting devices and gas sensors based on luminescence quenching. The working principle of the MAPLE technique was used for the deposition of colloidal nanoparticles and nanorods, too. TiO2 colloidal nanoparticles (diameter: ∼10 nm) and nanorods (diameter: 5 nm; length: 50 nm) were diluted in deionised water (0.02 wt %) and toluene (0.016 wt %) respectively. The deposited nanostructures preserved dimensions and structural properties of the starting particles and the films showed very interesting electrical responses when exposed to oxidizing gases for sensing applications.     

Embedding ZnO nanorods into porous cellulose aerogels via a facile one-step low-temperature hydrothermal method

A facile effective one-step low-temperature hydrothermal approach was employed to in situ embed ZnO nanorods into the porous cellulose aerogels. Besides, the preparation of cellulose aerogels is based on a green NaOH/polyethylene glycol solution. The rod-like ZnO has average diameter of about 348 nm and length of about 1.49 μm, and displays wurtzite phase. Meanwhile, the scanning electron microscope and transmission electron microscopy observations confirm that the nanorods are tightly anchored to the aerogels matrixes, and exhibit good dispersion without dramatic agglomeration, indicating that the cellulose aerogels are a class of ideal green matrix materials to support nanoparticles. Moreover, the method might also be extended to fabricate other multifunctional cellulose-based nanocomposites.     

Initiated chemical vapor deposition of polymer films on nonplanar substrates

Thin polymer films are deposited on nonplanar geometries via initiated chemical vapor deposition (iCVD). Films in microtrenches exhibit step coverage of 0.85 for the highest aspect ratio trench studied here. An analytical model shows that the sticking probability of the initiating radical is a function of monomer surface concentration and takes values between 1.1 × 10^− 2 and 5.0 × 10^− 2 for the conditions studied here. These results indicate that iCVD proceeds via reaction of a vapor phase initiating radical with a surface adsorbed monomer. The high degree of conformality allows iCVD to be used to create patterns with features less than 10 µm by physically masking the substrate.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).     

玻璃表面超疏水性薄膜制备

采用溶胶-凝胶法,以三甲基氯硅烷、氢氟硅酸和水为先驱体,在玻璃基片上用提拉法制备出一种含有-CF3强疏水性基团的氟硅烷薄膜.通过红外光谱和扫描电镜对薄膜结构和表面形貌进行了表征和观察.并用接触角测定仪三甲基氯硅烷和氢氟硅酸在不同摩尔配比下薄膜疏水性能.结果表明该薄膜具有高度交联的不规则球状表面结构.当三甲基氯硅烷和氢氟硅酸的摩尔比为2.5:1时,薄膜具有超疏水性,对水滴的表面接触角可达156°.     

Preparation of transparent water-repellent films by radio-frequency plasma-enhanced chemical vapour deposition

Preparation of transparent water-repellent films was carried out using three kinds of fluoroalkyl silanes (FASs) by radio-frequency plasma-enhanced chemical vapour deposition. The effects of the reaction conditions on the structures and properties of the films were studied. The films prepared showed high water repellency like poly(tetrafluoroethylene). The contact angles for water drops were about 107 °. The obtained contact angles depended on the length of perfluoroalkyl groups (C_nF_{2n + 1}-) in FASs. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate the film properties. The existence of the fluorine-containing groups such as –CF₃, –CF₂– and > CF– was confirmed at the film surfaces. The contact angle decreased when oxygen was added to the plasma because of the decrease in the fluorine concentration in the deposited films by the decomposition of C–F bonds. The transmittance of the polycarbonate substrates coated using FASs was improved. The films also acted as an antireflective coating. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of amino-terminated substrates onto surface properties of cellulose esters and their interaction with lectins

Films of cellulose acetate butyrate (CAB) and carboxymethylcellulose acetate butyrate (CMCAB) were deposited from ethyl acetate solutions onto bare silicon wafers (Si/SiO₂) or amino-terminated surfaces (APS) by means of equilibrium adsorption. All surfaces were characterized by means of ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The presence of amino groups on the support surface favored the adsorption of CAB and CMCAB, inducing the orientation of most polar groups to the surface and the exposition of alkyl group to the air. Such molecular orientation caused increase of the dispersive component of surface energy (γ_s^d) and decrease of the polar component of surface energy (γ_s^p) of cellulose esters in comparison to those values determined for films deposited onto bare Si/SiO₂ wafers. Adsorption behavior of jacalin or concanavalin A onto CAB and CMCAB films was also investigated. The adsorbed amounts of lectins were more pronounced on cellulose esters with high (γ_s^p) and total surface energy (γ_s^t) values.     

One-step preparation of polystyrene colloidal crystal films with structural colors and high hydrophobicity

The formation of polystyrene (PS) sphere nanostructures through vertical deposition can provide large surface roughness, which effectively enhances the hydrophobicity of the films. Moreover, well-ordered PS sphere arrays bring about structural colors, which can be controlled through the sphere diameter. All the water contact angles of colloidal crystal films prepared from monodisperse PS sphere solutions with diameters from 225 to 605 nm were larger than 120°, showing highly hydrophobic character.     

Cellulose acetate fibers covered by CdS nanoparticles for hybrid solar cell applications

In this work cellulose acetate (CA) fibers with a diameter of approximately 1 μm were immersed in a cadmium sulfide (CdS) precursor solution. After 3 h the original white color CA fibers became yellow and maintained the same form, suggesting the deposition of CdS on fiber surface. SEM images showed that CA fibers were covered by uniformly sized CdS nanoparticles of approximately 100 nm. XRD and optical absorption spectra indicated that they contained mostly cubic crystalline phase with the optical band gap of 2.43 eV. CdS coated CA fibers, called CdS(CA) fibers, were dispersed in a polar dispersant (dimethyl sulfoxide, DMSO) and then mixed with a poly(3-hexylthiophene) (P3HT) solution in a non-polar solvent (dichlorobenzene, DCB). The mixture was cast onto a transparent conductive glass substrate (Indium–Tin–Oxide, ITO), and after solvent evaporation a thin layer of CdS(CA)–P3HT composite was formed. It is observed that the volume relation between the polar dispersant and non-polar solvent influences the solubility of the P3HT product in the composite coating and the photovoltaic performance of the corresponding cell as well. The mass ratio between CdS(CA) fibers and P3HT in the composite layer affects the optical absorption of the composite. The best photovoltaic performance was obtained in CdS(CA)–P3HT based cells with a volume relation between DCB and DMSO of 3.5–1, a mass ratio between CdS(CA) and P3HT of 1:1, and a rapid drying process for composite coatings.     

Polymer microspheres stabilized by titania nanoparticles

Polymer microspheres stabilized by titania nanoparticles were synthesized using a two-step Pickering emulsion polymerization process, in which nanosized titania nanoparticles were used as solid emulsifiers and building blocks. It gives a simple but novel route for the fabrication of functional inorganic/polymer hybrid materials with controlled microstructures. The final Pickering emulsion can be applied to various substrates forming continuous films with highly ordered nanosized to microsized TiO₂ protuberances across the films. Those films will have potential applications for photo-catalyst, water and air purification.     

Wetting of microcrystalline and nanocrystalline Ni substrates by molten Sn-3.5Ag-0.7Cu alloy

Wetting behavior of molten Sn-3.5Ag-0.7Cu drops on Ni substrates with micrometer and nanometer grains was investigated using a modified sessile drop method. The wettability was poorer while the interfacial reactivity and atomic diffusivity were stronger for the nanocrystalline substrates compared with those for the microcrystalline substrates. The enhanced diffusion of the Ni atoms from the nanocrystallites greatly promoted the nucleation of the intermetallic compounds (IMCs), leading to a much thicker reaction layer and a more distinct regional distribution of the IMCs. On the other hand, the immediately roughened interface greatly decelerated the spreading of the triple line.     

Thin film deposition on plastic substrates using silicon nanoparticles and laser nanoforming

Reduced melting temperature of nanoparticles is utilized to deposit thin polycrystalline silicon (c-Si) films on plastic substrates by using a laser beam without damaging the substrate. An aqueous dispersion of 5 nm silicon nanoparticles was used as precursor. A Nd:YAG (1064 nm wavelength) laser operating in continuous wave (CW) mode was used for thin film formation. Polycrystalline Si films were deposited on flexible as well as rigid plastic substrates in both air and argon ambients. The films were analyzed by optical microscopy for film formation, scanning electron microscopy (SEM) for microstructural features, energy dispersive spectroscopy (EDS) for impurities, X-ray photoelectron spectroscopy (XPS) for composition and bond information of the recrystallized film and Raman spectroscopy for estimating shift from amorphous to more crystalline phase. Raman spectroscopy showed a shift from amorphous to more crystalline phases with increasing both the laser power and irradiation time during laser recrystallization step.     

Surface-modification of cellulose nanowhiskers and their use as nanoreinforcers into polylactide: A sustainably-integrated approach

In this study, bionanocomposites based on renewable cellulose nanowhiskers (CNWs) as nanofillers and renewable poly(l-lactide) (PLA) as polymeric matrix were successfully and straightforwardly prepared using melt-extrusion technique. Due to the affinity difference between hydrophobic PLA and hydrophilic CNWs, the surface of CNWs was directly modified in aqueous suspension (pH = 5.4 – citrate buffer) at ambient temperature in the presence of functional trialkoxysilanes bearing various organic moieties (alkyl, amino, and (meth)acryloxy). The surface-functionalization of CNWs was first investigated using methacryloxy-based trialkoxysilane as model. The influence of parameters such as the amount of silane agents and the post-treatment conditions were optimized on the surface-modification of methacryloxy-modified CNWs. FT-IR, TEM, WAXS and XPS analyses provided further evidences about the efficiency of the surface-modifications of CNWs. In a subsequent step, the chemically modified CNWs were successfully incorporated into PLA by melt-extrusion in the absence of solvent, without any alterations of their nanostructure after melt-processing. The thermal/mechanical properties of the resulting bionanocomposites were determined and shown to be enhanced when silanized CNWs were used as nanofillers.     

Crosslinking of copolymer thin films by initiated chemical vapor deposition for hydrogel applications

The ability of initiated chemical vapor deposition to finely tune crosslinking densities in copolymer thin films has been used to develop a functional, reactive hydrogel system. The system consists of poly[maleic anhydride-co-dimethyl acrylamide-co-di(ethylene glycol) divinyl ether] films covalently attached to silicon substrates using the coupling agent 3-aminopropylethoxydimethylsilane. The swelling of the films in water is pH-dependent, with a maximum swelling ratio of 11 at pH = 8. The hydrogel was also functionalized with 0.1 M cysteamine solutions in 2-propanol for 30 min to convert 97% of the anhydride functional groups to carboxylic acid and amide functionalities, confirmed by XPS and Fourier transform infrared spectroscopy. The functionalization yielded free thiol groups at the surface, which were used to attach CdSe/ZnS core-shell semiconductor nanoparticles to the hydrogels.     

Creating “Smart” Surfaces Using Stimuli Responsive Polymers

Surfaces modified with stimuli‐responsive polymers (SRPs) dynamically alter their physico‐chemical properties in response to changes in their environmental conditions. The triggered control of interfacial properties provided by immobilized SRPs at the solid–water interface has application in the design of biomaterials, regenerable biosensors, and microfluidic bioanalytical devices. In this article, we briefly summarize recent research in this area, followed by two recent examples of research from our laboratory on stimuli‐responsive surfaces. First, we present a new assay to quantify the phase transition behavior of SRPs at the solid–water interface. This assay, which is based on the distance‐dependent colorimetric properties of gold nanoparticles, provides a technically simple and convenient method to determine the effect of different variables on the lower critical solution temperature (LCST) behavior of SRPs at the solid–water interface. Second, we show that stimuli‐responsive surfaces can be created by the immobilization of an elastin‐like polypeptide (ELP), a thermally responsive biopolymer, on a glass surface. We exploit the phase transition of the ELP at a surface to reversibly address an ELP fusion protein to a surface. This method, which we term thermodynamically reversible addressing of proteins (TRAP), enables the reversible, spatio‐temporal modulation of protein binding at the solid‐liquid interface, and will enable the realization of new bioanalytical applications.