Chensi Shen

Enhanced catalytic ability of chitosan–Cu–Fe bimetal complex for the removal of dyes in aqueous solution

In this study, despite the high adsorption ability, efficient catalytic activity of a chitosan–metal complex has been developed through the chelation of chitosan polymer with bimetals Cu(II) and Fe(III). The removal of C. I. Reactive Black 5 (RB 5) by the chitosan–Cu–Fe complex/H2O2 system was studied in the pH range from 4 to 12. The maximal dye removal rate was achieved at an optimal concentration of Cu and Fe in the chitosan–Cu–Fe matrix, demonstrating the combination of sorptive enrichment and catalytic degradation. The results indicated that TOC removal and discoloration of the dye achieved 89.9% and 96.5% in a short reaction time. The pH sensitivity of the chitosan complex, the effect of the coexisting ions and the adsorption of other anionic dyes were also studied. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were analyzed to study the structure of the chitosan bi-metal complex and a possible mechanism was proposed.

High-dispersive FeS2 on graphene oxide for effective degradation of 4-chlorophenol

A high-dispersive FeS2 micro-cube crystal on graphene oxide (FeS2@GO) was fabricated by a one-pot hydrothermal method. The catalytic degradation of 4-chlorophenol (4-CP) and its mechanism in a FeS2@GO-based Fenton system was investigated. Under acidic to slight alkaline conditions, FeS2@GO demonstrated an excellent capacity to remove 4-CP. More than 97% of 4-CP was eliminated within 60 min in pH 7.0 reaction solutions initially containing 0.2 g L−1 FeS2@GO, 128.6 mg L−1 4-CP and 100 mM H2O2 at 25 ± 1 °C, and the removal of 4-CP was further enhanced with increasing FeS2@GO loadings. In the meantime, the FeS2@GO also achieved lower iron leaching and a more complete TOC removal compared with pure synthetic FeS2 without graphene oxide. Furthermore, acetic acid and oxalic acid were identified as the primary products. The remarkable capacity of the FeS2@GO-based Fenton system in removing 4-CP displays its potential application in the treatment of organic compound-contaminated water.

Biopolymer-induced morphology control of brushite for enhanced defluorination of drinking water

Due to the relatively lower potential health risks as well as the good affinity for fluoride anion, calcium-based minerals have been widely carried out for the adsorption of fluoride. The improvement of adsorption capacity can be accomplished by regulation of particle size, shape and structure. Thus, here we report the controllable synthesis of petal-like nanosheets of brushite by using chitosan as a regulator. The addition of chitosan polymer in calcium precursor not only could serve ideal nucleation sites but also could play a vital role in confining the calcium phosphate aggregates and thus controlling the size of the brushite flakes. When the concentration of chitosan was 0.01wt%, the as-synthesized brushite showed nanosheet-structured with the dimensions ranged from 100 to 200nm and displayed outstanding fluoride adsorption capacity of 231.5mg/g according to the fitted Langmuir model, which was comparatively higher than that of the previously reported calcium-based adsorbents. Moreover, the pH change and common co-existing anions in solution almost presented less negative effect on the F- adsorption onto petal-like brushite nanosheets. We hope that these petal-like nanosheets based on green nanotechnology can help to achieve the intention of safe drinking water.

Preparation and properties of chitosan–metal complex: Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan-metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan-metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan-Fe(III) complex prepared by sulfate salts exhibited the best adsorption efficiency (100%) for various dyes in very short time duration (10min), and its maximum adsorption capacity achieved 349.22mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan-metal complex. SO42- ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process. Additionally, the pH sensitivity and the sensitivity of ionic environment for chitosan-metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan-metal complex can help not only in optimizing its use but also in designing new chitosan-metal based complexes.

Fabrication of MnOx heterogeneous catalysts from wet sludge for degradation of azo dyes by activated peroxymonosulfate

For dewatering and resource utilization of sewage sludge, catalyst preparation paralleled with sewage sludge dewatering, was explored. In order to obtain a better understanding of this strategy, an anaerobic sludge based MnOx catalyst (MnOx/HCAS) was characterized, and tested in activation of Oxone for dye degradation in aqueous solution. The multi-valence oxidation states of manganese were formed in MnOx/HCAS. The catalyst exhibits high catalytic activity towards Oxone for the degradation of dyes in aqueous solution. The kinetic data followed first order kinetics with an activation energy of 21.87 kJ mol−1. The evaluation of the reusability of MnOx/HCAS showed that MnOx/HCAS exhibited high stability in recycled tests without losing its activity. The removal of a variety of anionic dyes also demonstrates an excellent catalytic performance of MnOx/HCAS. To investigate stabilization of heavy metals in the catalyst, a leaching test was conducted, and the result showed that heavy metals can be solidified to prevent their leaching into solution. The effect of different kinds of wet sludge was investigated. And all these sludge based MnOx catalysts exhibit good catalytic performance with azo dyes with degradation rates more than 98%, which decides its unquestionable possibility for fabrication of MnOx heterogeneous catalysts from wet sludge and its practical applications.

Al-Doped chitosan nonwoven in a novel adsorption reactor with a cylindrical sleeve for dye removal: performance and mechanism of action

In order to overcome the inconvenience of solid/liquid separation of powdered adsorbents, a novel adsorption reactor with a cylindrical sleeve was designed to match the textile-pattern of chitosan nonwoven for the sake of easy separation, simple operation and high efficiency. Meanwhile, Al-doped chitosan nonwoven was prepared to enhance the adsorption ability of chitosan nonwoven through the chelation interaction between dyes and metal centers of the Al-doped chitosan nonwoven. In this system, the adsorption of C. I. Acid Red 73 into Al-doped chitosan nonwoven could maintain high efficiency in a wide pH range from 3 to 10, with a high maximum adsorption capacity of 260.03 mg g−1. Additionally, the studies of reusability, pH sensitivity, the effect of the coexisting ions and the adsorption of other organic dyes indicated that the Al-doped chitosan nonwoven fixed in as a cylindrical sleeve within a reactor was technically feasible, highly efficient, and implies a potential of practical application for dyeing effluent treatment.

Synergistic removal of dyes by Myrothecium verrucaria immobilization on a chitosan–Fe membrane

A green efficient strategy for the combination of biodegradation and adsorption methods is urgently desired nowadays to degrade dyes in an economical and effective way. In this study, a kind of novel, environmentally friendly and efficient hybrid for the fungus and chitosan–Fe membrane has been fabricated by the alginate approach. Myrothecium verrucaria I-5 and C-1, deuteromycete fungi capable of producing laccase to degrade dyes, have been used. It is found that the chitosan–Fe membrane can excellently immobilize the fungi mycelia and enzyme, and after the immobilization, the fungi and enzyme still maintain a high activity after the dye decolorization. Also, the immobilized fungi membranes have been proved to have a high efficiency for dye decolorization. Simultaneously, the decolorization ability of the crude enzymes, which are extracted from I-5 and C-1 medium, and the decolorization ability of chitosan–Fe membrane are also investigated, respectively. The results demonstrate that the dyes can be removed by the fungi and the membrane synergistically. In addition, different kinds of dyes are successfully removed with chitosan–Fe immobilized fungi membranes. These results demonstrate that dyes are first adsorbed on the chitosan–Fe membrane, decreasing the toxicity to the fungus, and then bio-degraded by the laccase produced from the fungi on the membrane.