In-situ constructing nanostructured magnesium ferrite on steel slag for Cr(VI) photoreduction

Covalent organic framework modified vermiculite for total Cr removal and subsequent recycling for efficient ciprofloxacin and NO photooxidation

Design and fabrication of feasible remediation composites for total Cr (Cr(T)) removal is still challenging but urgently required. Herein, eco-friendly expanded vermiculite (VE) is integrated with a photoactive covalent organic framework (COF) polymer, in which photoinduced electrons of surface anchored COF can freely transfer to Cr(VI) for chemical reduction, and layered expanded VE allows ion exchange between resultant Cr(III) cations and interlayered K+, Ca2+, Mg2+, Na+, etc. The Cr(T) removal capacities of the surface-modified VE with important parameters (solution pH value, initial Cr(VI) concentration, etc.) are discussed extensively to understand how to select the best conditions for optimum Cr(T) removal performance. More interestingly, from a circular economy view point, spent Cr-loading VE-based waste can serve as a photocatalyst towards oxidation conversion of ciprofloxacin and NO gas subsequently. Explanations for different effects on physicochemical properties as well as catalytic activities of the reused Cr-loading waste are given. This strategy could provide valuable and promising contribution towards the development of sustainable low-cost mineral materials for Cr(T) removal. These findings also shed new light on the research of recycling spent photocatalyst for resource and reutilization.

Synthesis of a Magnetic Carnation-like Hydroxyapatite/Basic Calcium Carbonate Nanocomposite and Its Adsorption Behaviors for Lead Ions in Water

Calcium-enriched compounds have great potential in the treatment of heavy-metal contaminated wastewater. Preparing stable basic calcium carbonate (BCC), which is a calcium-enriched compound, and applying it in practice is a great challenge. This work investigated the formation process of hierarchical hydroxyapatite (HAP)/BCC nanocomposites and their adsorption behaviors regarding lead ions (Pb2+). The morphology of the HAP/BCC nanocomposite was controlled by the addition of monododecyl phosphate (MDP). The carnation-like HAP/BCC nanocomposite was achieved with the addition of 30 g of MDP. The carnation-like HAP/BCC nanocomposite had a high Pb2+ adsorption capacity of 860 mg g-1. The pseudo-second-order and Freundlich model simulation results indicated that the adsorptions of Pb2+ on the nanocomposites belonged to the chemisorption and multilayer adsorption processes. The main effective adsorption components for the nanocomposites were calcium-enriched HAP and BCC. Through the Ca2+ ions exchanging with Pb2+, the HAP and BCC phases were converted to hydroxyl-pyromorphite (Pb-HAP) and hydrocerussite (Pb3(CO3)2(OH)2), respectively. The carnation-like HAP/BCC nanocomposite has great potential in the treatment of heavy metal ions. This facile method provides a new method for preparing a stable HAP/BCC nanocomposite and applying it in practice.

CO2-assisted 'Weathering' of Steel Slag-Derived Calcium Silicate Hydrate: A Generalized Strategy for Recycling Noble Metals and Constructing SiO2-Based Nanocomposites

The spent adsorbent loaded by toxic metals is a solid hazardous waste which could cause significant secondary pollution due to potential possible additional release of metal ions. Therefore, the main subject is direct reutilization of spent adsorbents which can further economically and realistically offer new features, like recycling metal adsorbed, or formation of functional SiO₂-based nanocomposites. The nanoporous structure and negative surface charges enable steel slag-derived amorphous calcium silicate hydrate (CSH) to retain effectively the incoming metal ions (e. g. Au³⁺, Ag⁺, Pd²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ce³⁺, Y³⁺, and Gd³⁺) by chemisorption. Sparked by natural carbonation 'weathering', which ultimately sequestrates atmospheric CO₂ by alkaline silicate minerals to leach calcium from mineral matrix, the decalcification reactions of metal-bearing CSH results in successful recovery of noble metals (Ag, Au, Pd) upon NaOH etching the resultant SiO₂ support. Further, SiO₂-based heterostructures, containing nanocrystalline metals (e. g. Au⁰, Ag⁰, Pd⁰, Fe⁰, Co⁰, Ni⁰, Cu⁰, and Zn⁰) or rare-earth oxides (e. g. CeO₂, Y₂O₃, and Gd₂O₃), are formed after reduction in H₂/Ar (5 vol% H₂) flow, which is also very important for the multipurpose immobilization of diverse hybrid materials on SiO₂ surface (e. g. Cu⁰-Ag⁰@SiO₂, Cu⁰-CeO₂@SiO₂, and Cu⁰-Ag⁰-CeO₂@SiO₂).