Polyacrylate stabilized ZVI/Cu bimetallic nanoparticles for removal of hexavalent chromium from wastewater

Versatility of copper-iron bimetallic nanoparticles fabricated using Hibiscus rosa-sinensis flower phytochemicals: various enzymes inhibition, antibiofilm effect, chromium reduction and dyes removal

Bimetallic nanoparticles (NPs) are considered superior in terms of stability and function with respect to its monometallic counterparts. Hence, in the present study Hibiscus rosa-sinensis flower extract was used to synthesis copper-iron bimetallic nanoparticles (HF-FCNPs). HF-FCNPs was characterized and its applications (biological and environmental) were determined. HF-FCNPs were spherical in shape with high percentage of copper inducted into the NPs. HF-FCNPs inhibited mammalian glucosidases [maltase (IC50: 548.71 ± 61.01 µg/mL), sucrase (IC50: 441.34 ± 36.03 µg/mL), isomaltase (IC50: 466.37 ± 27.09 µg/mL) and glucoamylase (IC50: 403.12 ± 14.03 µg/mL)], alpha-amylase (IC50: 16.27 ± 1.73 µg/mL) and acetylcholinesterase [AChE (IC50: 0.032 ± 0.004 µg/mL)] activities. HF-FCNPs showed competitive inhibition against AChE, maltase and sucrase activities; mixed inhibition against isomaltase and glucoamylase activities; whereas non-competitive inhibition against α-amylase activity. HF-FCNPs showed zone of inhibition of 16 ± 2 mm against S. mutans at 100 µg/mL concentration. HF-FCNPs inhibited biofilm formation of dental pathogen, S. mutans. SEM and confocal microscopy analysis revealed the disruption of network formation and bacterial cell death induced by HF-FCNPs treatment on tooth model of S. mutans biofilm. HF-FCNPs efficiently removed hexavalent chromium in pH-independent manner and followed first order kinetics. Through Langmuir isotherm fit the qmax (maximum adsorption capacity) was determined to be 62.5 mg/g. Further, HF-FCNPs removed both anionic and cationic dyes. Altogether, facile synthesis of HF-FCNPs was accomplished and its biological (enzyme inhibition and antibiofilm activity) and environmental (catalyst to remove pollutants) applications have been understood.

Recent advances in bimetallic nanoscale zero-valent iron composite for water decontamination: Synthesis, modification and mechanisms

The environmental pollution of water is one of the problems that have plagued human society. The bimetallic nanoscale zero-valent iron (BnZVI) technology has increased wide attention owing to its high performance for water treatment and soil remediation. In recent years, the BnZVI technology based on the development of nZVI has been further developed. The material chemistry, synthesis methods, and immobilization or surface stabilization of bimetals are discussed. Further, the data of BnZVI (Fe/Ni, Fe/Cu, Fe/Pd) articles that have been studied more frequently in the last decade are summarized in terms of the types of contaminants and the number of research literatures on the same contaminants. Five contaminants including trichloroethylene (TCE), Decabromodi-phenyl Ether (BDE209), chromium (Cr(VI)), nitrate and 2,4-dichlorophenol (2,4-DCP) were selected for in-depth discussion on their influencing factors and removal or degradation mechanisms. Herein, comprehensive views towards mechanisms of BnZVI applications including adsorption, hydrodehalogenation and reduction are provided. Particularly, some ambiguous concepts about formation of micro progenitor cell, production of hydrogen radicals (H·) and H2 and the electron transfer are highlighted. Besides, in-depth discussion of selectivity for N2 from nitrates and co-precipitation of chromium are emphasized. The difference of BnZVI is also discussed.

Novel amino-modified bamboo-derived biochar-supported nano-zero-valent iron (AMBBC-nZVI) composite for efficient Cr(VI) removal from aqueous solution

Biochar-supported nano-zero-valent iron (BC-nZVI) composites have been extensively investigated for the treatment of Cr(VI)-containing wastewater. However, the inherent oxygen-containing groups with negative charges on BC exhibit electrostatic repulsion of the electronegative Cr(VI) species, limiting Cr(VI) removal. To overcome this limitation, this study prepared and used amino-modified bamboo-derived BC (AMBBC) as a supporting matrix to synthesize a novel AMBBC-nZVI composite. The amino groups (-NH2) on AMBBC were easily protonated and transformed into positively charged ions (-NH3+), which favored the attraction of Cr(VI) to AMBBC-nZVI, enhancing Cr(VI) removal. The experimental results demonstrated that the Cr(VI) removal efficiency of AMBBC-nZVI was 95.3%, and that of BBC-nZVI was 83.8% under the same conditions. The removal of Cr(VI) by AMBBC-nZVI followed the pseudo-second-order kinetic model and Langmuir isotherm model and was found to be a monolayer chemisorption process. Thermodynamic analysis revealed that the Cr(VI) removal process was spontaneous and endothermic. The mechanism analysis of Cr(VI) removal indicated that under an acidic condition, the -NH3+ groups on AMBBC adsorbed the electronegative Cr(VI) species via electrostatic interaction, promoting the attachment of Cr(VI) on AMBBC-nZVI; the adsorbed Cr(VI) was then reduced to Cr(III) by Fe0 and Fe(II), accompanied by the formation of Fe(III); moreover, AMBBC allowed the electron shuttle of nZVI to reduce Cr(VI); finally, the Cr(III) and Fe(III) species deposited on the surface of AMBBC-nZVI as Cr(III)-Fe(III) hydroxide coprecipitates.