Preparation of magnetic sodium alginate/sodium carboxymethylcellulose interpenetrating network gel spheres and use in superefficient adsorption of direct dyes in water

The rapid development of the printing and dyeing industry has led to the production of a large amount of high-density printing and dyeing wastewater, and technology for its effective treatment has become a focus of research. To construct a polymeric adsorbent material with abundant functional groups for the efficient adsorption of dye wastewater, a novel magnetic sodium alginate/carboxymethylcellulose interpenetrating network gel sphere (Fe3O4@SA/CMC-Fe) was prepared by co-blending sodium alginate (SA) and sodium carboxymethylcellulose (CMC) with Fe3O4; Fe3O4@SA/CMC-Fe was characterized by SEM-EDS, XRD, TGA, FT-IR, UV-Vis, VSM, BET-BJH and XPS. Static adsorption experiments showed that the optimal rates for adsorption of DV 51 and DR 23 from solutions with neutral pH values by Fe3O4@SA/CMC-Fe were up to 96 %, the adsorption process exhibited a Langmuir adsorption isotherm, and the dynamic adsorption process was accurately described by the pseudo-second-order kinetic model. A thermodynamic study showed that the adsorption reactions were all spontaneous exothermic reactions with increasing entropy. The mechanism for adsorption of the dyes by Fe3O4@SA/CMC-Fe involved hydrogen bonding, complexation and electrostatic adsorption. In summary, Fe3O4@SA/CMC-Fe is a green, simple, recyclable and highly efficient magnetic adsorbent that is expected to be widely used in treating dye wastewaters over a wide pH range.

Polyethylene glycol-modified mesoporous zerovalent iron nanoparticle as potential catalyst for improved reductive degradation of Congo red from wastewater

In this study, bare zero-valent iron nanoparticles (nZVI) have been modified using polyethylene glycol (PEG) of various molecular weight in a facile technique. The synthesized nZVI modified with PEG, M.W. of 600 and 6000 was denoted by nZVI-PEG₆₀₀ and nZVI-PEG₆₀₀₀, respectively, and compared their catalytic activity towards the reductive degradation of Congo red (CR) using NaBH₄.The existence of PEG layer surrounds the nZVI core was confirmed by several characterization tools, such as XRD, FTIR, FESEM and TEM. Herein, both nZVI-PEG₆₀₀ and nZVI-PEG₆₀₀₀ exhibited remarkable removal efficiencies of 89.6% and 99.2% within 14 min of reaction time. The optimum reaction parameters were found to be as follows: 0.2 g L^-1 catalyst dose and initial dye concentration of 2 × 10^-5 molL^-1 etc. Kinetic studies of dye degradation were investigated which follow pseudo-1^st-order kinetics. The TOC analysis confirmed the complete mineralization of CR dye by nZVI-PEG₆₀₀₀ nanocatalyst. GCMS analysis of plausible degraded products was performed to elucidate a probable mechanistic pathway of CR degradation. Further, we have investigated the degradation of two anionic dyes mixture, i.e., CR and methyl orange (MO) using best catalyst, i.e., nZVI-PEG₆₀₀₀.

Synthesizing nanoparticles of zinc and copper ferrites and examining their potential to remove various organic dyes through comparative studies of kinetics, isotherms, and thermodynamics

Nanoparticles of zinc ferrite (ZnFe₂O₄) and copper ferrite (CuFe₂O₄) were synthesized, and characterized, and these materials were applied for removal of organic dyes of alizarin yellow R (AYR), thiazole yellow G (TYG), Congo red (CR), and methyl orange (MO) from industrial wastewater through adsorption technique. Synthesis of ZnFe₂O₄ and CuFe₂O₄ was achieved through chemical co-precipitation method. These nanomaterials were characterized for physicochemical properties using XRD, FTIR, BET, VSM, DLS, Zeta-potential, and FESEM-EDX analytical instruments. BET surface areas of ZnFe₂O₄ and CuFe₂O₄ were 85.88 m²/g and 41.81 m²/g, respectively. Adsorption-influencing parameters including effect of solution pH, adsorbent quantity, initial concentration of dye pollutant, and contact time were examined. Acidic medium of the solution favored higher percentage of removal of dyes in wastewater. Out of different isotherms, Langmuir equilibrium isotherm showed the best fit with experimental data, indicating monolayer adsorption in the treatment process. The maximum monolayer adsorption capacities were found as 54.58, 37.01, 29.81, and 26.83 mg/g with ZnFe₂O₄, and 46.38, 30.06, 21.94, and 20.83 mg/g with CuFe₂O₄ for AYR, TYG, CR, and MO dyes, respectively. From kinetics analysis of the results, it was inferred that pseudo-second-order kinetics were fitting well with better values of coefficient of determination (R²). The removal of four organic dyes from wastewater through adsorption technique using nanoparticles of ZnFe₂O₄ and CuFe₂O₄ was observed to be spontaneous and exothermic. From this experimental investigation, it has been inferred that magnetically separable ZnFe₂O₄ and CuFe₂O₄ could be a viable option in removal of organic dyes from industrial wastewater.

Conductive-polymer-supported palladium-iron bimetallic nanocatalyst for simultaneous 4-chlorophenol and Cr(VI) removal: Enhanced interfacial electron transfer and mechanism

Nanoscale zerovalent iron (nZVI) reduction offers a wide range of applications in source-zone remediation, but the reactivity of nZVI is largely hampered due to its low electron-transfer ability and tendency to aggregate. Based on the dual function of conductive polymers (CPs) as support and electron transfer carrier, we combined CPs with nZVI and prepared a series of Pd/Fe bimetallic materials that successfully address the challenges of nZVI reduction. These Pd/Fe@CPs particles showed strong catalytic ability for the simultaneous removal of 4-chlorophenol (4-CP) and Cr(VI). The removal rate of 4-CP was significantly enhanced by 1.5-6.2 times after supporting Pd/Fe nanoparticles (NPs) with CPs. The enhanced reactivity of supported Pd/Fe NPs was attributed to their highly stabilized and dispersed state and the promoted electron transfer due to the synergistic effect between CPs and nZVI bimetallic particles. The various catalytic activity over Pd/Fe@CPs was attributed to the distinctive properties of CPs and their different interfacial electron transfer ability. Importantly, this study provides insights into distinguishing both mechanisms of direct electron transfer and atomic-hydrogen-mediated indirect electron transfer, and their quantitative relationship to the dehalogenation performance over Pd/Fe@CPs materials. This work provides better understanding of the remediation process and mechanisms of nZVI reduction.

Removal of organic compounds by nanoscale zero-valent iron and its composites

During the latest several decades, the continuous development of the economy and industry has brought more and more serious organic pollutants to the natural environment, which have inevitably aroused severe menace to human health and the environmental system. The nano zero-valent iron (NZVI) particles and NZVI-based materials have widely applied to remove organic pollutants. This article reviews the key advancements of different methods for the synthesis of NZVI and NZVI-based materials. Different modification methods (e.g., doped NZVI, encapsulated NZVI and supported NZVI) are also introduced detailedly for overcoming the defects of NZVI such as aggregation and easy oxidation. The removal of different organic pollutants including dyes, halogenated organic compounds, nitro-organic compounds, phenolic compounds, pesticides, and antibiotics are summarized. The interaction mechanisms, including adsorption, reduction, and active oxidation of organic pollutants by NZVI/NZVI-based composites, are discussed. The dyes are mainly removed by destroying their chromogenic group according to the reduction or the Fenton-like reaction with NZVI. The removal of halogenated organic compounds (HOCs) is realized by the dehalogenation process, including reductive elimination, hydrogenolysis, and hydrogenation. As for the nitro-organic compounds, three different reduction pathways as nitro-reduction (into amino), cleavage at the carbon‑nitrogen bond or denitration of the NO₂ group may take effect. The phenolic compounds can be mineralized into inorganic molecules, including CO₂ and H₂O, by Fenton oxidation. This review might provide the basis for future studies on developing more effective NZVI-based materials for the treatment of wastewaters contaminated by organic pollutants.

Zero Valent Iron Nanoparticle-Loaded Nanobentonite Intercalated Carboxymethyl Chitosan for Efficient Removal of Both Anionic and Cationic Dyes

A zero valent iron-loaded nano-bentonite intercalated carboxymethyl chitosan (nZVI@nBent-CMC) composite was fabricated and characterized by FT-IR, TEM, TEM-EDX, XRD, BET surface area, and zeta potential measurements. The as-fabricated nZVI@nBent-CMC composite exhibited excellent removal efficiency for both anionic Congo red (CR) dye and cationic crystal violet (CV) dye. The maximum uptake capacities of CR and CV onto the nZVI@nBent-CMC composite were found to be 884.95 and 505.05 mg/g, respectively. The adsorption process of both dyes well fitted with the Langmuir isotherm model and pseudo-second order kinetic model. Thermodynamic data clarified that the adsorptions of both CR and CV onto the nZVI@nBent-CMC composite are spontaneous processes. Moreover, the adsorption of CR onto the nZVI@nBent-CMC composite was found to be an exothermic process while that of CV is an endothermic process. The nZVI@nBent-CMC composite also exhibited excellent reusability for both studied dyes without noticeable loss in the removal efficiency, suggesting its validity to remove both anionic and cationic dyes from wastewater.

Application of a new type of Si–Al porous clay material as a solid phase support for immobilizing Acidovorax sp. PM3 to treat domestic sewage

A novel Si–Al porous clay material W (reprocessed from ceramic waste) was used for Acidovorax sp. strain PM3 immobilization to promote the growth of strains and improve nitrogen and phosphorus removal performance in water treatment systems. The porous clay material W was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy indicating that porous clay material W was a type of mullite with 63.52 m2/g specific surface area. After immobilization, the maximum biomass increased 2.7 times the specific growth rate and the removal rates of chemical oxygen demand (COD), ammonia (NH4+–N), and total phosphorus (TP) by the immobilized PM3 were 42.99, 29.19, and 11.76% higher than the free strain after 24 h. The Monod equation showed that the growth rate and processing speed of immobilized PM3 increased. The maximum adsorption capacities of COD and NH4+–N onto porous clay material W were 2.33 and 0.32 mg/g on the basis of Langmuir isotherm. The removal capacities of COD, NH4+–N, and TP by the immobilized PM3 were 588.24, 20.37, and 5.06 mg/l, respectively, as shown by kinetic studies. These results demonstrated that porous clay material W could improve the efficiency of microbial nitrogen and phosphorus removal, and the immobilized microorganism system could effectively treat domestic sewage. The adsorption isotherms can well describe the adsorption process. The maximum adsorption capacity of COD and NH4+–N on porous clay material W is 2.33 and 0.32 mg/g, respectively. Kinetic studies showed that the removal capacity of immobilized PM3 to COD, NH4+–N, and TP was 58.824, 20.37, and 5.06 mg/l, respectively.