Fabrication of Iron-Containing Biochar by One-Step Ball Milling for Cr(VI) and Tetracycline Removal from Wastewater

A novel graphene oxide functionalized hydrocalumite/cellulose composite for the selective and simultaneous removal of tetracycline and Cr(VI)

Tetracycline antibiotic and hexavalent chromium removal from the wastewater is crucial for preventing future environmental trouble. This study aimed to develop an eco-friendly biocomposite made from an enhanced graphene oxide-functionalized hydrocalumite/cellulose composite for co-adsorbative removal of TC antibiotic and toxic Cr(VI). The synthesized GO@CellHC composite was characterized using various microscopic techniques. The GO@CellHC composite possessed the superior removal for TC and Cr(VI), achieving 27.4 and 42.6 mg/g in single systems, and 24.8 and 39.6 mg/g in binary systems, all within 40 min. In pH results, the maximum removal was observed at an acidic pH of 3 for Cr(VI) and 5 for TC, respectively. The co-ions results demonstrated that the composite efficiently removed both pollutants, except in the presence of PO43- and CO32-. The Langmuir isotherm indicated the strongest adsorption capacity and favored both systems. Thermodynamic studies revealed that the adsorption of both systems onto the GO@CellHC composite removes TC and Cr(VI) by endothermic and spontaneous system. Kinetic results demonstrated that TC adsorption showed a higher rate constant k2 (single: 0.01676 min-1 and binary: 0.0138 min-1) compared to Cr(VI) adsorption (single: 0.01478 min-1 and binary: 0.01007 min-1). The GO@CellHC composite retained more than 80 % after three cycles, and field results suggesting that the biocomposite can be utilized for the removal of binary water pollutants.

Synthesis of Porous Red Mud/Slag-Based Spherical Geopolymers for Efficient Methylene Blue and Ni2+ Removal from Water

To reuse red mud and slag wastes as raw materials, a green type of porous spherical red mud/slag-based geopolymer (RSG) was synthesized by utilizing suspension curing and foaming techniques. Because methylene blue (MB) and nickel ion (Ni2+) were common and difficult to treat in wastewater, the adsorption characteristics of MB and Ni2+, as well as the phase and microstructure of the porous RSG spheres prior to and after adsorption, were thoroughly investigated. The porous RSG spheres showed a stable and mesoporous structure with a BET surface area of 31.36 m2/g. The spheres achieved the maximum removal efficiencies of 99.81% (MB) and 99.01% (Ni2+) at dosages of 16 and 10 g/L, respectively. The pseudo-second-order kinetic model and the Langmuir model could match the adsorption data of these spheres, with predicted maximum adsorption capacity (Qmax) values of 19.88 mg/g for MB and 12.39 mg/g for Ni2+, respectively. After three adsorption-desorption cycles, porous RSG spheres demonstrated good recycling capability with removal efficiencies of 98.10% (MB) and 54.60% (Ni2+). The spheres were also effective in adsorbing additional dyes (methyl orange (MO), crystal violet (CV), and malachite green (MG)) and heavy metal ions (Cd2+, Pb2+, Zn2+, and Cu2+). The spheres have potential use in water treatment.

Urban wastewater disinfection by FeCl3-activated biochar/peroxymonosulfate system: Escherichia coli inactivation and microplastics interference

Biochar coupled with peroxymonosulfate (PMS) to produce sulfate radicals and its application to urban wastewater disinfection has been rarely investigated and no information is available about microplastics (MPs) interference on the disinfection process. In this study, FeCl3-activated biochar (Fe-BC) was coupled to PMS to evaluate the inactivation of Escherichia coli (E. coli) in real secondary treated urban wastewater. Surface morphology of Fe-BC sample, characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), showed a rough texture with uniform distribution of iron particles over the entire surface area. E. coli inactivation improved (∼3.8 log units, detection limit = 1 CFU/100 mL) as Fe-BC concentration was decreased (from 1.0 g/L to 0.5 g/L), at a constant PMS dose (300 mg/L). Besides, removal efficiency of E. coli was negatively affected by the presence of small (30-50 μm) polyethylene MPs (PE MPs) (200 mg/L), which could be attributed to the adsorption of MPs on Fe-BC surface, according to SEM images of post-treated Fe-BC. The low disinfection efficiency of Fe-BC/PMS system in presence MPs could be due to blocking of Fe-BC sites for PMS activation and/or radicals scavenging during treatment. These results allowed to unveil the mechanisms of MPs interference on E. coli inactivation by Fe-BC/PMS, as well as the potential of this process to make the effluent in compliance with the stringent limit for agricultural reuse.

Insights into the Mechanism of Efficient Cr(VI) Removal from Aqueous Solution by Iron-Rich Wheat Straw Hydrochar: Coupling DFT Calculation with Experiments

Agricultural solid waste has become one of the raw materials for hydrothermal carbon production, promoting resource utilization. This study synthesized two types of ball-milling carbons (Fe-MHBC vs MHBC) with and without FeCl3 modification using wheat straw hydrochars. Cr(VI) adsorption on these two types of ball-milling carbons was investigated. According to Langmuir's maximum adsorption capacity analysis, Fe-MHBC had a capacity of 116.29 mg g-1. The thermodynamic analysis based on isothermal adsorption reveals the spontaneous process of the reaction between the two materials. The adsorption of Cr(VI) on Fe-MHBC exhibited excellent agreement with the pseudo-second-order kinetics model. Furthermore, X-ray photoelectron spectroscopy analysis showed that Fe(II) in the material reduced Cr(VI) when it participated in the reaction. The acidic conditions facilitate the elimination of Cr(VI). The Fe-MHBC has a higher zeta potential, which enhances the electrostatic attraction of Cr(VI) particles. Even with a starting pH of 10, the removal rate can be consistently maintained at over 64%. The adsorption of Cr(VI) was inhibited by various anions and higher ion concentrations. Density functional theory demonstrates that the presence of Fe enhances the adsorption capacity and electron transfer flux of Cr(VI). Fe-MHBC effectively eliminates Cr(VI) by the process of electrostatic adsorption, redox, and complexation reactions. This study demonstrated that hydrochar materials modified by FeCl3 through a ball-milling process show considerable potential as effective adsorbents in the treatment of Cr(VI) pollution, offering a viable and environmentally friendly solution for mitigating this prevalent environmental issue.

Amino-Functionalized Lotus Stem Hydrochar for Rapid Adsorption and In Situ Detoxification of Cr(VI) from Water

The development of low-cost, efficient, and environmentally friendly adsorbents is the key to highly toxic hexavalent chromium [Cr(VI)] removal by adsorption. In this paper, amino-functionalized lotus stem hydrochar (ALSHC) was prepared from an agricultural waste lotus stem (LS) for the adsorption removal of Cr(VI) from water. The effects of the initial Cr(VI) concentration, contact time, temperature, coexisting anions, and reusability of ALSHC on Cr(VI) removal were examined in detail. The adsorption mechanism was further discussed by investigating the impact of the solution's initial pH, the relation between the pH change in solution and Cr(VI) removal during the process, the changes of chromium (Cr) species in solution and on ALSHC during adsorption, and the XPS characterization. The results demonstrated that ALSHC effectively removed Cr(VI) from water with rapid adsorption (the removal rate reached 80.90% in only 10 min) and in situ detoxification. Most importantly, ALSHC still had better adsorption performance (adsorption capacity of 30.95 mg g-1) than commercially activated carbon, even at pH = 9.00. The adsorption of Cr(VI) by ALSHC accorded with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating a monolayer chemisorption process. The adsorption process was shown to be spontaneous and endothermic based on the thermodynamic characteristics (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0). The mechanism of Cr(VI) removal was mainly composed of three parts in sequence: Firstly, Cr(VI) in solution was quickly adsorbed onto ALSHC with protonated -NH2 through electrostatic attraction; subsequently, the adsorbed Cr(VI) on ALSHC was mostly detoxicated by in situ reduction; and finally, the reduced Cr(III) and the remaining Cr(VI) were fixed on the ALSHC surface by complexation. The prepared ALSHC displayed a certain superiority in Cr(VI) adsorption and had the prospect of further development.