Zhujian Huang

Enhancement of photocatalytic degradation of dimethyl phthalate with nano-TiO2 immobilized onto hydrophobic layered double hydroxides: A mechanism study

The organic layered double hydroxides (LHDs)/TiO(2) composites with various mass ratios were prepared by the reconstruction of mixed metal oxides to photodegrade dimethyl phthalate (DMP). The physicochemical properties of the obtained products were analyzed by X-ray diffraction (XRD) spectra, X-ray photoelectron spectra (XPS), UV-vis diffuse reflectance spectroscope and scanning electron microscope (SEM). The results showed that the TiO(2) particles and the organic LDHs were combined together through chemical bonds, and TiO(2) particles were well distributed on the surface of the interconnecting organic LDHs nano-flakes. According to the experimental results of adsorptive and photodegradation of DMP, the organic LDHs with flaky structure could effectively adsorb the DMP molecules and the adsorption isotherm by the composites modeled well with the Langmuir equation. The enrichment of DMP onto the composites and the external hydroxyl groups of the composites produce a synergistic effect leading to greatly enhance the rate of DMP photocatalytic degradation by the obtained composites.

Fabrication and photocatalytic properties of a visible-light responsive nanohybrid based on self-assembly of carboxyl graphene and ZnAl layered double hydroxides

The synthesis of a layer-by-layer ordered nanohybrid with a sandwich structure was based on electrostatically driven self-assembly between the negatively charged carboxyl graphene monolayer and the positively charged ZnAl-layered double hydroxide nanosheets. The characteristics of the layer-by-layer ordered nanohybrid were investigated by SEM, TEM, AFM and XRD. The enhanced photocatalytic activity of the calcined product was determined by the photocatalytic degradation of the cationic dye methylene blue (MB) and anionic dye orange G (OG) under visible light. The enhanced photocatalytic efficiency was mainly attributed to the effective electronic coupling between graphene and calcined ZnAl-LDH. Additionally, the chemical stability of the calcined ZnAl-LDH is significantly improved by hybridization of graphene and this is attributed to the protection provided by the close contacted graphene with highly stability. This work also establishes a simple method for fabricating graphene-based nanohybrids with a sandwich structure.

Efficient removal of cesium from aqueous solution with vermiculite of enhanced adsorption property through surface modification by ethylamine

Ethylamine modified vermiculite (Ethyl-VER) with high specific surface area and excellent pore structure was prepared to remove cesium from aqueous solution. The physic-chemical properties of the pristine and modified vermiculite were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), specific surface area (BET) and scanning electron microscopy/energy disperse spectroscopy (SEM/EDS). The corroding effect of ethylamine increased the specific surface area of vermiculite from 4.35 to 15.59 m(2) g(-1), and the average pore diameter decreased from 6.8 to 5.34 nm. Batch adsorption experiments were conducted as a function of pH, initial Cs(+) concentration, contact time, coexisting cations (K(+), Na(+), Ca(2+)) and low-molecular-weight organic acids (acetic acid, oxalic acid, citric acid) to illustrate the adsorption behavior. The study found that the adsorption capacity of cesium in aqueous solution was improved from 56.92 to 78.17 mg g(-1) after modification. The formation of micropores and mesopores and the increased surface area played a critical role in the enhancement of cesium adsorption. Kinetic experiments indicated that the adsorption process can be simulated well with a pseudo-second-order model. The presence of cations or low-molecular-weight organic acids inhibited cesium adsorption in different degrees. On the basis of our results, Ethyl-VER with good surface characteristics and high adsorption capacity is a suitable adsorbent for cesium removal from aqueous solution.

Enhanced dechlorination performance of 2,4-dichlorophenol by vermiculite supported iron nanoparticles doped with palladium

In this study, environment-friendly vermiculite (VMT) was used to support nanoscale zero-valent iron (nZVI) and nZVI doped with palladium (abbreviated as Fe-VMT and Pd/Fe-VMT, respectively). The physicochemical properties of the products obtained were analyzed by X-ray diffraction (XRD), specific surface area (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the BET surface areas of Fe-VMT and Pd/Fe-VMT were 39.5 m2 g−1 and 59.1 m2 g−1, and 18.9 m2 g−1 for unsupported nZVI nanoparticles. The presence of vermiculite led to a decrease in the aggregation of nZVI and Pd/Fe as observed by SEM and TEM. Batch experiments were conducted to investigate the catalytic performance of nZVI, Pd/Fe, VMT, Fe-VMT and Pd/Fe-VMT via the dechlorination reaction of 2,4-dichlorophenol (2,4-DCP). The dechlorination rates of 2,4-DCP by Pd/Fe-VMT (by adding Pd) were greater than that achieved by Fe-VMT. Additionally, the dechlorination of 2,4-DCP by Pd/Fe-VMT would be influenced by temperature, initial pH values, Pd loading, initial concentration of 2,4-DCP and the dosage of materials. It was confirmed that the ultimate reduction product of 2,4-DCP was phenol. Overall, Pd/Fe-VMT is a promising material for the dechlorination of 2,4-DCP.

Synthesis and catalytic properties of La or Ce doped hydroxy-FeAl intercalated montmorillonite used as heterogeneous photo Fenton catalysts under sunlight irradiation

A series of La and Ce doped hydroxyl FeAl intercalated montmorillonite (FeAl-Mt) were prepared by a co-intercalation method for catalytic oxidation of Reactive Blue 19 (RB19) by a heterogeneous photo Fenton process under natural sunlight irradiation. The physicochemical properties of the obtained catalysts were deciphered by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) and UV-vis diffuse reflectance spectroscopy (DRS). The results showed that Ce or La doped FeAl Keggin polyoxocations were intercalated into the gallery of montmorillonite and the physicochemical properties of intercalated FeAl Keggin polyoxocations were mildly changed after Ce or La doping, resulting in defects and lattice vacancies. The doping of Ce or La could effectively improve the catalytic performance of FeAl-Mt measured by heterogeneous photo Fenton degradation of RB19 catalyzed by the obtained products. The synergistic effect between the doped element and FeAl intercalated montmorillonite played a crucial role in the enhancement of heterogeneous catalytic activity under natural sunlight irradiation.

Decontamination of tetracycline by thiourea-dioxide–reduced magnetic graphene oxide: Effects of pH, ionic strength, and humic acid concentration

Thiourea-dioxide-reduced magnetic graphene oxide (TDMGO) was successfully prepared as an efficient adsorbent for the removal of tetracycline (TC) from aqueous solutions via strong adsorptive interactions. The composite was characterized by SEM, TEM, EDS, TGA, FT-IR, XPS, XRD and VSM. The effects of variables such as the pH, TC concentration, and temperature were successfully analyzed. The kinetics and isothermal parameters were described well by pseudo-second-order and Langmuir isotherm models, respectively, and the maximum adsorption capacity (qm) of TDMGO for TC calculated from the Langmuir isotherm was 1233mg/g at 313K. The removal of TC onto TDMGO, as indicated by the thermodynamic parameters, was spontaneous and endothermic. The removal performance was slightly affected by the solution pH. The presence of NaCl in the solution facilitated TC adsorption, and the optimum adsorption capacity was obtained when the NaCl concentration was >0.001M. The adsorption capacity decreased slightly with increasing humic acid concentration. In addition, the adsorbent could be regenerated and reused. Based on these results, TDMGO is a promising adsorbent for the efficient removal of TC antibiotics from aquatic environments for pollution treatment.

Enhanced degradation of phenol by Sphingomonas sp. GY2B with resistance towards suboptimal environment through adsorption on kaolinite

The effects of clay minerals on microbial degradation of phenol under unfavorable environmental conditions were investigated. Degradation of phenol by Sphingomonas sp. GY2B adsorbed on kaolinite, montmorillonite, and vermiculite were evaluated in comparison with free bacteria under optimal conditions. Kaolinite was found to be the most effective in accelerating degradation rate (reducing the degradation time) as well as improving degradation efficiency (increasing the percentage of phenol degraded), with GY2B/kaolinite complex achieving a degradation efficiency of 96% within 6 h. GY2B adsorbed on kaolinite was more competent than free GY2B in degradation under conditions with high phenol concentrations and at alkaline pH. Kaolinite reduced the time required for degradation by 8-12 h and improved the degradation efficiency by as much as 82% at high phenol concentrations. Meanwhile, the GY2B/kaolinite complex reduced the degradation time by 24 h and improved the degradation efficiency by 46% at pH 12. The improvement was partially due to the buffering effects of kaolinite. It was also shown that Cr(VI) and kaolinite synergistically enhanced the degradation by GY2B, with Cr(VI) and kaolinite both increasing the degradation rate and kaolinite being primarily responsible for enhanced degradation efficiency. These results showed one of the common clay minerals, kaolinite, is able to significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. Kaolinite can collaborate with Cr(VI) to further improve the microbial degradation performance. It is implied that clay minerals have great potential to be applied in enhancing the biodegradation of phenol.

Efficient inhibition of heavy metal release from mine tailings against acid rain exposure by triethylenetetramine intercalated montmorillonite (TETA-Mt).

The potential application of triethylenetetramine intercalated montmorillonite (TETA-Mt) in mine tailings treatment and AMD (acid mine drainage) remediation was investigated with batch experiments. The structural and morphological characteristics of TETA-Mt were analyzed with XRD, FTIR, DTG-TG and SEM. The inhibition efficiencies of TETA-Mt against heavy metal release from mine tailings when exposed to acid rain leaching was examined and compared with that of triethylenetetramine (TETA) and Mt. Results showed that the overall inhibition by TETA-Mt surpassed that by TETA or Mt for various heavy metal ions over an acid rain pH range of 3-5.6 and a temperature range of 25-40°C. When mine tailings were exposed to acid rain of pH 4.8 (the average rain pH of the mining site where the mine tailings were from), TETA-Mt achieved an inhibition efficiency of over 90% for Cu(2+), Zn(2+), Cd(2+) and Mn(2+) release, and 70% for Pb(2+) at 25°C. It was shown that TETA-Mt has a strong buffering capacity. Moreover, TETA-Mt was able to adsorb heavy metal ions and the adsorption process was fast, suggesting that coordination was mainly responsible. These results showed the potential of TETA-Mt in AMD mitigation, especially in acid rain affected mining area.

Enhanced photo-degradation of bisphenol a under simulated solar light irradiation by Zn–Ti mixed metal oxides loaded on graphene from aqueous media

In the present study, the mixed metal oxides (rGO-ZnTi-MMO-x, x presents weight percentage of GO) were obtained by thermal treatment of a Zn–Ti layered double hydroxides-graphene oxide (GO-ZnTi-LDHs) composite. rGO-ZnTi-MMOs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectra techniques. The photocatalytic activity of the obtained photocatalysts showed significantly enhanced activities in the degradation of bisphenol A (BPA). Compared with pristine ZnTi-MMOs, 88.12% of BPA at 10 mg L−1 was degraded using 0.5 g L−1 of rGO-ZnTi-MMO-2% as a catalyst under 3 h of simulated solar light irradiation. Photo-generated holes, ˙OH and singlet oxygen radicals were demonstrated to be the predominant active species responsible for the photo-degradation of BPA. UV-vis diffuse reflectance spectra, photoluminescence spectra electrochemical impedance spectroscopy and transient photocurrent response of the photocatalyst confirmed that the enhanced photocatalytic activity of rGO-ZnTi-MMOs composites was attributed to the extended visible light absorption region and efficient transportation and separation of photo-induced electron–hole pairs of rGO-ZnTi-MMOs with unique hetero-nanostructure. Therefore, this work presents a facile method for the fabrication of a kind of graphene-based photocatalyst for water treatment.

Successful intercalation of DNA into CTAB-modified clay minerals for gene protection

Montmorillonite (MMT) and rectorite (REC) are clay minerals that consist of hydrated aluminum silicate with Si–O tetrahedrons on the bottom of the layer, Al–O(OH)2 octahedrons on the top, and various exchangeable ions such as Na+ and Ca2+ in interlayer. However, the driving force for intercalation of double-stranded DNA is not sufficient to open up the gallery of MMT and REC and allows the intercalation to occur. Furthermore, the external surface of MMT and REC is hydrophilic rather than organophilic. In the study, cationic hexadecyl trimethyl ammonium bromide (CTAB) is chosen to modify MMT and REC to make clay minerals more compatible with DNA. CTAB intercalates into the galleries of clay minerals and expands the basal spacing for DNA intercalation. Novel CTAB-clay/DNA hybrids are synthesized for the first time, with their structure investigated by X-ray diffraction and Fourier transform infrared. Gel electrophoresis analysis confirms that the CTAB-modified clay could protect DNA from degradation of DNase I. UV absorption spectroscopy and circular dichroism indicate that the modified clay minerals can provide a capacity for protecting DNA from damage induced by heavy metals. In addition, the intercalated DNA can be recovered readily under alkaline conditions. Therefore, CTAB-clay/DNA hybrids are potential materials for storage of genetic information.