Efficiency of Ppy-PA-pani and Ppy-PA composite adsorbents in Chromium(VI) removal from aqueous solution

Removal of hexavalent chromium from wastewater by chelating resin supported Fe/Cu bimetallic nanoparticles: Characterization, performance and mechanisms

In this work, Bimetallic Fe/Cu nanoparticles were successfully stabilized by chelating resin, which was specifically employed for the remediation of hexavalent chromium contaminated wastewater. Based on the characterization results, it was observed that the Fe/Cu bimetallic nanoparticles were uniformly and well distributed on the surface of the resin DOW M4195. The results demonstrated that the supported bimetallic Fe/Cu nanoparticles exhibited an excellent performance for Cr(VI) removal efficiency, reaching up to 99.4%. A series of factors, including initial pH, initial concentration of Cr(VI), co-exciting ions and humic acid were systematically evaluated to ascertain their respective impacts on Cr(VI) removal. The kinetics study followed intra-particle diffusion model demonstrated that both the adsorption and diffusion processes of Cr(VI) by the DOW M4195 resin played an important role in the overall removal of Cr(VI). The analytical results derived from XPS spectra at specific reaction times revealed the underlying removal mechanism of Cr(VI): Cr(VI) was adsorbed onto M-Fe/Cu due to the rich porous structure of the chelating resin DOW M4195. Additionally, the presence of the second metal, Cu, was found to significantly enhance the reduction performance of Fe0 and Fe(II) during the Cr(VI) removal process. The Cr(VI) removal mechanism was determined to involve a combination of physical adsorption, redox reactions and co-precipitation.

Surface-bound Fe(0) and Fe(II) mediated by 2-picolinic acid functionalized zero-valent iron for highly Cr(VI) removal

Electron transfer of zero-valent iron (ZVI) is significantly impeded by its oxide layer, and limiting its removal of pollutants. In this study, 2-picolinic acid (PA) and ZVI were co-ball milled to improve electron transfer in ZVI (PA-ZVIbm), and used for the removal of heavy metal Cr(VI). Characterization analysis showed that the presence of electron-rich groups on the surface of PA-ZVIbm promoted the transfer of electrons from the Fe(0) core to the surface, and the surface Fe(0) and Fe(II) contents increased from 1.1 % to 6.3 % and from 60.2 % to 72.9 %, respectively, effectively reducing Cr(VI) through an electron transfer mechanism. Theoretical calculations showed that the modification of PA enhanced the adsorption of Cr(VI) on the ZVI surface, and the adsorption energy decreased from -3.561 eV to -5.119 eV. PA-ZVIbm showed strong advantages in the removal of Cr(VI), with a reaction rate constant and adsorption capacity 17 and 13 times that of ZVIbm, respectively, and a conversion rate of 100 %. Moreover, PA-ZVIbm showed excellent performance over a wide pH range (3-10) and under different coexisting ions, while being cost-effective and having low environmental risks. This study explored the relationship between ZVI surface modification and performance, and provided new insights into the modification of ZVI using small molecule oxygen-containing organic acids.

Exploring bio-remediation strategies by a novel bacteria Micrococcus sp. strain HX in Cr(VI)-contaminated groundwater from long-term industrial polluted

Hexavalent chromium (Cr(VI)) has emerged as a contaminant of heavy metal, owing to its wide use in industry. This study focuses on elucidating the interaction between microbial communities and environmental parameters in Cr(VI)-contaminated groundwater near a factory in Henan Province, and evaluating the bio-remediation potential of microorganisms toward Cr(VI) reduction. The highest concentration of Cr(VI) in the groundwater is 208.08 mg/L. The dominant microbes were Proteobacteria and Bacteroidota, closely positively related to Cr(VI) and SO42-. Many of these genus have been proven to be chromium tolerant or have the ability to reduce Cr(VI). Two strains, Micrococcus sp. HX and Bacillus sp. HX-2, were isolated from contaminated groundwater, and Micrococcus sp. HX was used for the first time to reduce Cr(VI) in groundwater. The reduced ability of HX reached 90.18 % at a Cr(VI) concentration of 100 mg/L, while HX-2 achieved a reduction capacity of 63.8 %. Micrococcus sp. HX shows the best reduction efficiency in alkaline environments (ph=8), which is close to the tannery industry wastewater. The reduction efficiency by Micrococcus sp. HX reached 67.26 % in groundwater samples (Cr(VI)= 26.08 mg/L). Transcriptome analyses revealed oxidoreductase activity, ATP binding and the NAD(P) binding region protein-related gene expression were up-regulated. Binding reduction experiments indicated that most of the Cr(III) was detected extracellular, which suggests that the reduction of Cr(VI) by HX was mainly extracellular enzyme-catalyzed.

Sequential removal of phosphate and copper(II) ions using sustainable chitosan biosorbent

Although adsorbents are good candidates for removing phosphorus and heavy metals from wastewater, the use of biosorbents for the sequential treatment of phosphorus and copper has not yet been studied. Porous chitosan (CS)-based biosorbents (CGBs) were developed to adsorb phytic acid (PA), a major form of organic phosphate. This first adsorbate (PA) further served as an additional ligand (P-type ligand) for the CGBs (N-type ligand) to form a complex with the second adsorbate (copper). After the adsorption of PA (the first adsorbate), the spent CGBs were recycled and used as a new adsorbent to adsorb Cu(II) ions (the second adsorbate), which was expected to have a dual coordination effect through P, N-ligand complexation with copper. The interactions and complexation between CS, PA and Cu(II) ions on the PA-adsorbed CGBs (PACGBs) were investigated by performing FTIR, XPS, XRD, and SEM-EDS analyses. The PACGBs exhibited fast and enhanced adsorption of Cu(II) ions, owing to the synergistic effect of the amino groups of CS (the original ligand, N-type) and the phosphate groups of PA (an additional ligand, P-type) on the adsorption of Cu(II) ions. This is the first time that sequential removal of phosphorus and heavy metals by biosorbents has been performed using biosorbents.

Improving U(VI) retention efficiency and cycling stability of GCN-supported calcined-LDH composite: Mechanism insight and real water system applications

The synthesis and characterization of graphitic carbon nitride (GCN) and its composites with calcined layered double hydroxide (CLDH) were examined in this investigation. The goal was to assess these composites' maximum adsorption capacity (qmax) for U(VI) ions in wastewater. Several different characterization methodologies were utilized to examine the fabricated substances. These methods encompass X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The GCN-CLDH composite displayed enhanced adsorption ability towards U(VI) ions due to its high surface functionality. Langmuir adsorption isotherm analysis showed that more than 99% of U(VI) ions were adsorbed, with a qmax of 196.69 mg/g. The kinetics data exhibited a good fit for a pseudo-second-order (PSO) model. Adsorption mechanisms involving precipitation and surface complexation via Lewis's acid-base interactions were proposed. The application of the GCN-CLDH composite in groundwater demonstrated adsorption below the maximum permissible limit established by USEPA, indicating improved cycling stability. These observations underscore the capacity of the GCN-CLDH composite's proficiency in adsorbing U(VI) aqueous solutions containing radioactive metals.

PANI/MCM-41 adsorption for removal of Cr(VI) ions and its application in enhancing electrokinetic remediation of Cr(VI)-contaminated soil

In this study, a polyaniline/mesoporous silica (PANI/MCM-41) composite material that can be used as a filler for permeable reactive barrier (PRB) was prepared by in situ polymerization. Firstly, the adsorption capacity of PANI/MCM-41 on Cr (VI) in solution was investigated. The results show that the prepared PANI/MCM-41 exhibits a significant Cr (VI) adsorption capacity (~ 340 mg/g), and the adsorption process is more accurately described by the Langmuir isotherm and pseudo-second-order kinetic model. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. In addition, adsorption-desorption cycle experiments proved the excellent reusability of the material. Subsequently, the material was utilized as a filler in the PRB for the remediation of Cr(VI)-contaminated soil using electrokinetic-permeable reactive barrier (EK-PRB) technology. The results show that compared with traditional electrokinetic remediation, the use of PANI/MCM-41 as an active filler can enlarge the current during remediation and enhance the conductivity of soil, which increases the removal rates of total Cr and Cr(VI) in soil (17.4% and 10.2%).