Nano-manganese oxides-modified biochar for efficient chelated copper citrate removal from water by oxidation-assisted adsorption process

A new strategy for utilization of gasification ash: Manganese oxides-modified activated carbon for efficient copper citrate removal

To address the challenges posed by solid waste generated from coal gasification ash, a pyrolysis self-activation method was employed to prepare activated carbon by gasification ash, followed by the modification with manganese oxide to enhance its adsorption performance. Subsequently, the removal efficiency and mechanism for copper citrate were investigated. The results demonstrated the successful preparation of manganese oxides modified gasification ash-derived activated carbon (GAC-MnOx), exhibiting a specific surface area of 158.3 m2/g and a pore volume of 0.1948 cm³/g. The kinetic process could be described by the pseudo-second-order kinetic model (R2 = 0.958). High removal efficiency and low concentration of dissolved Mn were observed within the pH range of 3-10, where the adsorption capacity of GAC-MnOx for copper citrate exhibited an inverse relationship with pH. Notably, the fitting results of the Langmuir model demonstrated that the maximum adsorption capacity of GAC-MnOx for copper citrate is determined to be 7.196 mg/g at pH 3. The adsorption capacity of GAC-MnOx was found to be significantly reduced to 0.26 mg/g as the pH decreased below 2, potentially attributed to the dissolution of Mn. The findings of the Dual-Mode model demonstrated that the copper citrate removal mechanism by GAC-MnOx involved both surface adsorption and precipitation processes as follows: the porous structure of activated carbon enables physical adsorption of copper citrate, the MnOx or oxygen-containing functional groups establish chemical bonds with copper citrate and subsequently precipitate onto the surface of the adsorbent. The physical adsorption remains predominant in the removal of copper citrate, despite a gradual decrease in its proportion with increasing pH and equilibrium concentrations. Moreover, the X-ray photoelectron spectroscopy results indicated that copper citrate might be oxidized by MnOx to release copper ions and be retained on the surface of the adsorbent, meaning the adsorption efficiency of Cu(II)-Cit by GAC was enhanced through MnOx oxidation. This study could provide a new strategy for the high-value resource utilization of gasification ash.

Advances in the adsorption of heavy metal ions in water by UiO-66 composites

The innovative adsorbents known as the Metal-organic Framework (MOFs) had a high specific surface area, various structural types, and good chemical stability. MOFs have been produced through hydrothermal, mechanochemical, microwave-assisted, gelation, and other synthesis methods, and the solvothermal process is one of them that researchers frequently utilize. The UiO materials have a more comprehensive application potential than different subtypes of MOFs among the numerous MOFs that have been synthesized. The synthesis of MOFs and their composites, as well as the adsorption characteristics of UiO materials in the adsorption of various heavy metal ions, have all been examined and summarized in this study.

Remediation of As-contaminated soils using citrate extraction coupled with electrochemical removal

Arsenic (As) pollution of soils poses serious threats to the ecological environment. In this study, organic acid (citrate) washing and electrochemical removal (manganese oxide cathode) were combined to remediate highly As-contaminated soils, and the effect of voltage was investigated as well. Citrate could extract the As bound to iron and aluminum oxides and enhance As mobility by indirectly reducing As(V) to As(III) in the soils. During the electrochemical removal of As, the rhodochrosite produced from the reduction of birnessite at the cathode, the birnessite generated from the re-oxidation of released Mn(II) and the ferrihydrite formed from the hydrolysis of Fe(III) at the anode together contributed to the adsorption and fixation of As in the leachate. After three successive rounds of combined remediation by citrate (0.1 mol L^-1) washing and electrochemical removal with birnessite electrode at 1.5 V, the As was totally removed in the leachate and the content of As bound to iron and aluminum (hydr)oxides was reduced by 84.2% in soils. Correspondingly, the contents of total and bioavailable As in the soil decreased from 1981.4 and 242.0 to 563.2 and 86.0 mg kg^-1, respectively. The As removal efficiency from the leachate and soil increased with increasing voltage from 0 to 1.5 V. This study provides a new method for the effective treatment of As-contaminated soils.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.

Highly Efficient Removal for Methylene Blue and Cu2+ onto UiO-66 Metal-Organic Framework/Carboxylated Graphene Oxide-Incorporated Sodium Alginate Beads

Herein, we report a new metal-organic framework (MOF)-based composite beads adsorbent made via incorporating UiO-66 MOF, carboxylated graphene oxide (GOCOOH) into sodium alginate for efficient removal of methylene blue dye, and Cu2+ ions. The successful fabrication of the synthesized UiO-66/GOCOOH@SA composite beads was confirmed by means of X-ray diffraction, Fourier transform infrared, scanning electron microscopy, zeta potential, X-ray photoelectron spectroscopy analysis, and thermogravimetric analysis and BET measurement. The incorporation of both UiO-66 and GOCOOH into SA beads greatly increased their adsorption efficiency for the removal of both MB and Cu2+ with maximum adsorption capacities of 490.72 and 343.49 mg/g, respectively. The removal process of both MB and Cu2+ follows the pseudo-second-order model and Freundlich isotherm model. A plausible adsorption mechanism was discussed in detail. Regeneration tests clarified that the removal efficiencies toward both MB and Cu2+ remained higher than 87% after five cycles. These results reveal the potentiality of UiO-66/GOCOOH@SA beads as an excellent adsorbent.

Removal of copper ions by functionalized biochar based on a multicomponent Ugi reaction

Copper is widely present in the natural environment and inevitably poses a risk to both human health and the natural environment. Biochar is an inexpensive, clean and sustainable sorbent material that can be used as a resource for copper removal, and there is interest in new ways to chemically treat biochar to tune its unique properties and modify its atomic structure. In this study, biochar was oxidized, and then polyethyleneimine (PEI) modified chitosan and carboxylated biochar were economically compounded through a multicomponent Ugi reaction to effectively remove Cu(ii). PEI enhances the adsorption of Cu(ii) within an optimum solution pH range of 3.5–5.5. The adsorption process follows a pseudo-second-order kinetic model. When the dosage of BC-NH2 was 4 g L⁻¹ and the temperature was 303 K, the maximum adsorption capacity calculated by the Langmuir model was 26.67 mg g⁻¹. The adsorption process of Cu(ii) on BC-NH2 was heat-trapping and spontaneous. BC-NH2 showed good selectivity for K⁺ and Mg²⁺, and BC-NH2 desorbed by NaOH showed better adsorption performance than H₂SO₄ in the adsorption–desorption cycle. Characterization by SEM, EDS, BET, FTIR, TGA and XPS showed successful coupling and that the amide group of BC-NH2 had chelated with Cu(ii). This atomically economical multicomponent Ugi reaction provides a new option for preparing composite materials that effectively remove heavy metals.

Polyethyleneimine-modified chitosan and carboxylated biochar were economically compounded by a multicomponent Ugi reaction to produce products rich in amide functional groups.

Formation and mechanisms of nano-metal oxide-biochar composites for pollutants removal: A review

Biochar, a carbon-rich material, has been widely used to adsorb a range of pollutants because of its low cost, large specific surface area (SSA), and high ion exchange capacity. The adsorption capacity of biochar, however, is limited by its small porosity and low content of surface functional groups. Nano-metal oxides have a large SSA and high surface energy but tend to aggregate and passivate because of their fine-grained nature. In combining the positive qualities of both biochar and nano-metal oxides, nano-metal oxide-biochar composites (NMOBCs) have emerged as a group of effective and novel adsorbents. NMOBCs improve the dispersity and stability of nano-metal oxides, rich in adsorption sites and surface functional groups, maximize the adsorption capacity of biochar and nano-metal oxides respectively. Since the adsorption capacity and mechanisms of NMOBCs vary greatly amongst different preparations and application conditions, there is a need for a review of NMOBCs. Herein we firstly summarize the recent methods of preparing NMOBCs, the factors influencing their efficacy in the removal of several pollutants, mechanisms underlying the adsorption of different pollutants, and their potential applications for pollution control. Recommendations and suggestions for future studies on NMOBCs are also proposed.