A fully bio-sourced adsorbent of heavy metals in water fabricated by immobilization of quinine on cellulose paper

Experimental study on evaluation and optimization of heavy metals adsorption on a novel amidoximated silane functionalized Luffa cylindrica

This study aimed to synthesize an amidoximated Luffa cylindrica (AO-LC) bioadsorbent, and evaluate its efficiency in the adsorption of heavy metals from the aqueous solutions. For this purpose, NaOH solution was used to alkaline treatment of Luffa cylindrica (LC) fibers. The silane modification of LC was performed using 3-(trimethoxysilyl)propyl methacrylate (MPS). Polyacrylonitrile (PAN)/LC biocomposite (PAN-LC) was synthesized by PAN grafting onto the MPS-modified LC (MPS-LC). Finally, the AO-LC was obtained by the amidoximation of PAN-LC. The chemical structures, morphology, and thermal properties of biocomposites were characterized by the infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy. The results showed a successful grafting of MPS and PAN on the surface of LC. The order of heavy metals adsorption on AO-LC was: Pb²⁺ > Ag⁺ > Cu²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺. The effects of operational parameters on the Pb²⁺ adsorption were studied using Taguchi experimental design method. Statistical analysis of the results showed that the initial Pb²⁺ concentration and the bioadsorbent dosage significantly affect the adsorption efficiency. The adsorption capacity and removal percentage of Pb²⁺ ions were obtained as 18.88 mg/g and 99.07%, respectively. The Langmuir isotherm and Pseudo-second order kinetics models were found to be better compatible with experimental data as a consequence of the isotherm and kinetics analysis.

Heavy metal-contained wastewater in China: Discharge, management and treatment

A large amount of heavy metal-contained wastewater (HMW) was discharged during Chinese industry development, which has caused many environmental problems. This study reviewed discharge, management and treatment of HMW in China through collecting and analyzing data from China's official statistical yearbook, standards, technical specifications, government reports, case reports, and research paper. Results showed that industry wastewater discharged by an amount of about 221.6 × 10⁸ t (in 2012), where emission of heavy metals including Pb, Hg, Cd, Cr(VI), T-Cr was around 388.4 t (in 2012). Heavy metal emission with wastewater in east China and central south China was observed to be graver than that in other areas. However, control of heavy metals in Pb and Cd in northwest China was more difficult compared with other areas. In terms of management, China's government has issued many wastewater discharge standards, strict management policies for controlling HMW discharge in recent years, resulting in reduced HMW discharge. In addition, main HMW treatment technology in China was chemical precipitation, and other technologies such as membrane separation, adsorption, ion exchange, electrochemical and biological methods were also occasionally applied. In the future, chemical industries will be concentrated in northwest China, therefore control of HMW discharge should be paid much more attention in those areas. In addition, more effective and environment-friendly heavy metal removal and regeneration technologies should be developed, such as biomaterials adsorbent.

Developing flow photo-thiol–ene functionalizations of cinchona alkaloids with an autonomous self-optimizing flow reactor

Continuous flow photo-thiol–ene reactions on cinchona alkaloids with a variety of organic thiols have been developed using enabling technologies such as a self-optimizing flow photochemical reactor.

Fabrication and Application of SERS-Active Cellulose Fibers Regenerated from Waste Resource

The flexible SERS substrate were prepared base on regenerated cellulose fibers, in which the Au nanoparticles were controllably assembled on fiber through electrostatic interaction. The cellulose fiber was regenerated from waste paper through the dry-jet wet spinning method, an eco-friendly and convenient approach by using ionic liquid. The Au NPs could be controllably distributed on the surface of fiber by adjusting the conditions during the process of assembling. Finite-difference time-domain theoretical simulations verified the intense local electromagnetic fields of plasmonic composites. The flexible SERS fibers show excellent SERS sensitivity and adsorption capability. A typical Raman probe molecule, 4-Mercaptobenzoicacid (4-MBA), was used to verify the SERS cellulose fibers, the sensitivity could achieve to 10⁻⁹ M. The flexible SERS fibers were successfully used for identifying dimetridazole (DMZ) from aqueous solution. Furthermore, the flexible SERS fibers were used for detecting DMZ from the surface of fish by simply swabbing process. It is clear that the fabricated plasmonic composite can be applied for the identifying toxins and chemicals.

Mathematical modelling of the influence of physico-chemical properties on heavy metal adsorption by biosorbents

Adsorption rate is a critical parameter in the design of effective biosorbent treatment systems for heavy metals removal. Though numerous studies have identified the physico-chemical properties of biosorbents that exert influence on the adsorption rate, such influence has not been mathematically defined, limiting the effective design of adsorption systems. This study quantifies the influence of biosorbent physico-chemical properties including, specific surface area, surface functional groups, pore size, pore volume and zeta potential on the adsorption rate in relation to three divalent metal cations. Mathematical equations were developed to predict the influence of physico-chemical properties on pseudo second order kinetic constant and thereby predict the adsorption rate. Tea factory waste and coconut shell biochar were mixed in different weight percentages to vary the physico-chemical properties under consideration. Four different initial metal ion concentrations were used. Relationship between pseudo second order kinetic constant at each concentration with physico-chemical properties was quantified using regression analysis. The experimental analysis revealed that among the physico-chemical properties, acidic surface functional groups had the most profound influence on sorption mechanisms. Reliability and accuracy of the predictive models were significantly improved when separate models were developed for two ranges of initial metal ion concentrations. The outcomes of this study will contribute to the effective design and optimization of biosorbent mixtures with the capacity to remove Pb²⁺, Cu²⁺ and Cd²⁺ in wastewater.

Efficient removal of Cr(VI) from water by the uniform fiber ball loaded with polypyrrole: Static adsorption, dynamic adsorption and mechanism studies

A novel adsorbent, the uniform fiber ball (UFB) loaded with polypyrrole (UFB-PPy), was synthesized for Cr(VI) removal from water in this paper. The structure of the UFB and UFB-PPy were characterized by SEM, EDS, FT-IR, BET, XPS and TG. The adsorption properties of UFB-PPy towards Cr(VI) were investigated by the effects of temperature, initial concentration of Cr(VI), interfering ions and contact time in batch experiments, the isothermal models (Langmuir, Freundlich and Temkin) and the kinetic models (Pseudo first-order kinetic, Pseudo second-order kinetic and Intra-particle diffusion models) were used to describe the adsorption behavior. The effects of the initial concentration and flow rate of the Cr(VI) solution in the column experiments were also studied, and the dynamic models (Yoon-Nelson, Adams-Bohart and Wolborska model) were applied to predict the adsorption performance. The Cr(VI) removal mechanism of UFB-PPy was revealed by studying the effect of pH on adsorption, testing of Cl^-, and analyzing the XPS. The results showed that UFB-PPy exhibited excellent adsorption properties for Cr(VI) both in batch and column adsorption. The possible adsorption mechanism involved electrostatic attraction, ion exchange and reduction. Conveniently, the chromium resources can be recovered with the form of high-purity Cr₂O₃ by simple calcination of Cr(VI)-captured UFB-PPy (UFB-PPy-Cr).