Shuilin Zheng

Characterization and improved solar light activity of vanadium doped TiO2/diatomite hybrid catalysts

V-doped TiO2/diatomite composite photocatalysts with different vanadium concentrations were synthesized by a modified sol-gel method. The diatomite was responsible for the well dispersion of TiO2 nanoparticles on the matrix and consequently inhibited the agglomeration. V-TiO2/diatomite hybrids showed red shift in TiO2 absorption edge with enhanced absorption intensity. Most importantly, the dopant energy levels were formed in the TiO2 bandgap due to V(4+) ions substituted to Ti(4+) sites. The 0.5% V-TiO2/diatomite photocatalyst displayed narrower bandgap (2.95 eV) compared to undoped sample (3.13 eV) and other doped samples (3.05 eV) with higher doping concentration. The photocatalytic activities of V doped TiO2/diatomite samples for the degradation of Rhodamine B under stimulated solar light illumination were significantly improved compared with the undoped sample. In our case, V(4+) ions incorporated in TiO2 lattice were responsible for increased visible-light absorption and electron transfer to oxygen molecules adsorbed on the surface of TiO2 to produce superoxide radicals ˙O2(-), while V(5+) species presented on the surface of TiO2 particles in the form of V2O5 contributed to e(-)-h(+) separation. In addition, due to the combination of diatomite as support, this hybrid photocatalyst could be separated from solution quickly by natural settlement and exhibited good reusability.

Synthesis, characterization and activity of an immobilized photocatalyst: natural porous diatomite supported titania nanoparticles

Diatomite, a porous non-metal mineral, was used as support to prepare TiO2/diatomite composites by a modified sol-gel method. The as-prepared composites were calcined at temperatures ranging from 450 to 950 °C. The characterization tests included X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with an energy-dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption/desorption measurements. The XRD analysis indicated that the binary mixtures of anatase and rutile exist in the composites. The morphology analysis confirmed the TiO2 particles were uniformly immobilized on the surface of diatom with a strong interfacial anchoring strength, which leads to few drain of photocatalytic components during practical applications. In further XPS studies of hybrid catalyst, we found the evidence of the presence of Ti-O-Si bond and increased percentage of surface hydroxyl. In addition, the adsorption capacity and photocatalytic activity of synthesized TiO2/diatomite composites were evaluated by studying the degradation kinetics of aqueous Rhodamine B under UV-light irradiation. The photocatalytic degradation was found to follow pseudo-first order kinetics according to the Langmuir-Hinshelwood model. The preferable removal efficiency was observed in composites by 750 °C calcination, which is attributed to a relatively appropriate anatase/rutile mixing ratio of 90/10.

Degradation of simazine from aqueous solutions by diatomite-supported nanosized zero-valent iron composite materials.

A novel composite material based on deposition of nanosized zero-valent iron (nZVI) particles on acid-leached diatomite was synthesised for the removal of a chlorinated contaminant in water. The nZVI/diatomite composites were characterised by X-ray diffraction, scanning electron microscopy, elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Compared with the pure nZVI particles, better dispersion of nZVI particles on the surface or inside the pores of diatom shells was observed. The herbicide simazine was selected as the model chlorinated contaminant and the removal efficiency by nZVI/diatomite composite was compared with that of the pristine nZVI and commercial iron powder. It was found that the diatomite supported nZVI composite material prepared by centrifugation exhibits relatively better efficient activity in decomposition of simazine than commercial Fe, lab synthesised nZVI and composite material prepared via rotary evaporation, and the optimum experimental conditions were obtained based on a series of batch experiments. This study on immobilising nZVI particles onto diatomite opens a new avenue for the practical application of nZVI and the diatomite-supported nanosized zero-valent iron composite materials have potential applications in environmental remediation.

XRD, TEM, and thermal analysis of Arizona Ca-montmorillonites modified with didodecyldimethylammonium bromide.

An Arizona SAz-2 calcium montmorillonite was modified by a typical dialkyl cationic surfactant (didodecyldimethylammonium bromide, abbreviated to DDDMA) through direct ion exchange. The obtained organoclays were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution thermogravimetric analysis (HR-TG), and infrared emission spectroscopy (IES). The intercalation of surfactants greatly increased the basal spacing of the interlayers and the conformation arrangement of the loaded surfactant were assessed based on the XRD and TEM measurements. This work shows that the dialkyl surfactant can be directly intercalated into the montmorillonite without first undergoing Na(+) exchange. Moreover, the thermal stability of organoclays and the different arrangements of the surfactant molecules intercalated in the SAz-2 Ca-montmorillonite were determined by a combination of TG and IES techniques. The detailed conformational ordering of different intercalated surfactants under different conditions was also studied. The surfactant molecule DDDMA has proved to be thermally stable even at 400°C which indicates that the prepared organoclay is stable to significantly high temperatures. This study offers new insights into the structure and thermal stabilities of SAz-2 Ca-montmorillonite modified with DDDMA. The experimental results also confirm the potential applications of organic SAz-2 Ca-montmorillonites as adsorbents and polymer-clay nanocomposites.

Synthesis of a novel illite@carbon nanocomposite adsorbent for removal of Cr(VI) from wastewater

A novel illite@carbon (I@C) nanocomposite adsorbent has been synthesized via a facile hydrothermal carbonization process (HTC) using glucose as carbonaceous source and illite as the carrier. The morphology, microstructure and surface properties of the prepared nanocomposite adsorbent were analyzed by FESEM, TGA, XRD, FT-IR and Zeta potential measurements. Batch experiments were carried out on the adsorption of Cr(VI) to determine the adsorption properties of the composite. The adsorption of Cr(VI) onto the I@C nanocomposite was well described by the pseudo-second-order kinetic model and Langmuir isotherm. Compared with the illite and carbon material (SC) separately, the prepared I@C nanocomposite adsorbent exhibited enhanced adsorption performance for Cr(VI) with a maximum adsorption capacity of 149.25mg/g, which was higher than that of most reported adsorbents. In addition, the adsorption process was spontaneous and endothermic based on the adsorption thermodynamics study. The adsorption of Cr(VI) by I@C was highly pH-dependent and the optimum adsorption occurred at pH2.0. The Zeta potential analysis results indicated that the electrostatic interactions between anionic Cr(VI) and the positively charged surface of the adsorbent might be critical to the adsorption mechanism. This study demonstrated that the I@C nanocomposite should be a promising candidate for a low-cost, environmental friendly and highly efficient adsorbent for the removal of toxic Cr(VI) from wastewater.

A comparative study of different diatomite-supported TiO2 composites and their photocatalytic performance for dye degradation

AbstractThree kinds of diatomites as catalyst carriers were adopted to prepare supported TiO2 catalysts by a typical hydrolysis–deposition method. The prepared composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption–desorption, scanning electron microscopy transmission electron microscopy, UV–vis diffuser reflectance, and chemical oxygen demand. The photocatalytic properties of composites were determined using rhodamine B, methyl orange, and methylene blue as target pollutants under UV light irradiation. A comparative study on the photocatalytic properties of composite catalysts was carried out. It is indicated that the catalytic performance of TiO2/diatomite is significantly influenced by the physicochemical properties of diatomite supports. Compared with pure TiO2, the TiO2/diatomite composites exhibited smaller crystalline size of TiO2 and better dispersibility, which induced higher specific surface area and better photo-degradation efficiency. The hig...

Facile synthesis of two clay minerals supported graphitic carbon nitride composites as highly efficient visible-light-driven photocatalysts

To overcome rapid electron-hole recombination and low adsorption capacity of single g-C3N4 photocatalyst, the present work reports on the fabrication of two kinds of visible-light-driven composite photocatalysts (g-C3N4/kaolinite and g-C3N4/illite composites). 2D/2D assembly was successfully achieved in this work. Furthermore, the as-synthesized composites exhibited significantly enhanced photocatalytic activity under visible-light irradiation, whose reaction rate constants were almost 4.13 times (g-C3N4/kaolinite) and 3.18 times (g-C3N4/illite) that of pure g-C3N4. A plausible reaction mechanism over the as-prepared composite photocatalysts was also proposed based on the experimental results obtained. The photocatalytic enhancement of synthesized composites should be attributed to the intimate interface contact between g-C3N4 and layered minerals, resulting in better dispersion performance, higher charge separation efficiency as well as stronger adsorption ability.

In situ synthesis of carbon @ diatomite nanocomposite adsorbent and its enhanced adsorption capability

ABSTRACT Carbon @ diatomite (C@DE) nanocomposite was synthesized using glucose as precursor and purified diatomite as carrier through a facile hydrothermal carbonization process. The microstructure and interface properties of the obtained nanocomposites were characterized by SEM, TEM, FTIR, XPS and zeta potential analyzer. A batch adsorption study showed that the adsorption process was very fast and the kinetic data well fitted with pseudo-second-order kinetic model. Compared to pure carbon materials, the C@DE nanocomposite exhibits higher adsorption ability for Cr (VI). This kind of nanocomposite is a promising candidate as an adsorbent for the removal of Cr (VI) ions from wastewater.

Simultaneous adsorption of aflatoxin B1 and zearalenone by mono- and di-alkyl cationic surfactants modified montmorillonites

Organo-montmorillonites (OMts) modified with mono- and di-alkyl cationic surfactants were prepared to remove polar mycotoxin aflatoxin B1 (AFB1) and weak polar, hydrophobic mycotoxin zearalenone (ZER) simultaneously. The structural and surface properties of the prepared OMts were investigated. In vitro adsorption experiments were carried out to simulate the in vivo conditions of gastrointestinal tract of animals by a batch mode. The adsorption of AFB1 and ZER in both single and binary-contaminate systems were investigated systematically. Both OMts showed super enhanced adsorption capacities towards AFB1 and ZER whenever in single and binary-contaminate systems compared with raw Mt, indicating the effectiveness of the prepared OMts acted as mycotoxins adsorbents. DODAC-Mt showed a higher adsorption capacity towards AFB1 and ZER than OTAB-Mt. The equilibrium data of AFB1 on OMts were fitted satisfactorily with Freundlich and Linear models, suggesting the co-existence of different adsorption mechanism which were proposed to be ion-dipole interactions (between surfactant cations and carbonyl groups of AFB1) and adsorption/partition mechanisms. The adsorption isotherms of OMts to ZER matched best with Linear models, implying the adsorption/partition mechanism. For simultaneous adsorption, the adsorption process of one mycotoxin was slightly affected by the presence of the other mycotoxin due to the requirement of partial same sorption sites. In addition, the solution pH had negligible influence on the adsorption process of OMts, meaning no desorption occurred when the adsorbents pass through from stomach to intestine as animal feed.

Evaluation of nonionic surfactant modified montmorillonite as mycotoxins adsorbent for aflatoxin B 1 and zearalenone

This work aims at exploring the potential of nonionic surfactant octylphenol polyoxyethylene ether (OP-10) modified montmorillonites (NMts) as mycotoxins adsorbent. The resulting NMts has different structural configurations, organic carbon contents, surface hydrophobicity and textural properties at different surfactant loadings. The prepared NMts were used for adsorption of polar aflatoxin B1 (AFB1) and weak polar zearalenone (ZER) in both single and binary-contaminate systems by simulating conditions of gastrointestinal tract. The adsorption capacities of NMts to AFB1 and ZER increased up to 2.78 and 8.54 mg/g respectively from 0.51 and 0.00 mg/g of raw montmorillonite (Mt). High adsorption capacities of NMts to AFB1 and ZER could be reached at low surfactant loadings. There was little decrease from pH of 3.5 to 6.5 but became negligible with increasing the surfactant loadings. In binary-contaminate adsorption system, the adsorption of ZER was obviously affected by the existence of AFB1, while ZER had little effect on the adsorption process of AFB1 due to different adsorption mechanism. This study demonstrates that NMts could be a promising adsorbent for simultaneous detoxification of polar and non-polar mycotoxins.