Polyamide-baghouse dust nanocomposite for removal of methylene blue and metals: Characterization, kinetic, thermodynamic and regeneration

Adsorptive removal of organic pollutants from aqueous solutions using novel GO/bentonite/MgFeAl-LTH nanocomposite

The contamination of water with organic pollutants such as dyes and phenols is a serious environmental problem, requiring effective treatment methods. In the present study, a novel nanocomposite was synthesized by intercalating graphene oxide and bentonite clay into MgFeAl-layered triple hydroxide (GO/BENT/LTH), which was characterized using different techniques. The adsorption efficacy of the GO/BENT/LTH nanocomposite was assessed via the removal of two harmful organic water pollutants, namely methyl orange (MO) and 2-nitrophenol (2NP). The obtained results revealed that the maximum adsorption capacities (qmax) of MO and 2NP reached 3106.3 and 2063.5 mg/g, respectively, demonstrating the excellent adsorption performance of the nanocomposite. Furthermore, this study examined the effects of contact time, initial MO and 2NP concentrations, pH, and temperature of the wastewater samples on the adsorptive removal of MO and 2NP by the GO/BENT/LTH nanocomposite. The pH, zeta potential, and FTIR investigations suggested the presence of more than one adsorption mechanism. Thermodynamic investigations elucidated the exothermic nature of the adsorption of MO and 2NP onto the GO/BENT/LTH nanocomposite, with MO adsorption being more sensitive to temperature change. Additionally, regeneration studies revealed a marginal loss in the MO and 2NP removal with the repetitive use of the GO/BENT/LTH nanocomposite, demonstrating its reusability. Overall, the findings of this study reveal the promise of the GO/BENT/LTH nanocomposite for effective water decontamination.

Adsorption mechanism of methylene blue by magnesium salt-modified lignite-based adsorbents

The rich pore structure and carbon structure of lignite make it a suitable adsorbent for effectively removing methylene blue (MB) from wastewater. This article reports the preparation of lignite-based adsorbents modified by magnesium salts, and the key factors and adsorption mechanism are analyzed to effectively improve the adsorption performance for MB. The results showed that the lignite was modified by magnesium salts, and the Mg2+ in the magnesium salts had a good binding effect on the oxygen-containing functional groups in the lignite. This improved the adsorption performance of the lignite-based adsorbents for MB. The Mg(NO3)2-modified lignite-based adsorbent showed the best adsorption performance and removal rate of MB (99.33%) when prepared with 8 wt % Mg(NO3)2. Characterization analysis showed that a "-COOMg" structure was formed between Mg2+ in the magnesium salts and the carboxylic acid functional group in the lignite, which was postulated to be the absorption site that promoted the adsorption performance for MB. It is speculated that the MB adsorption mechanism of this lignite-based adsorbent is ion exchange.

Fabrication porous adsorbents templated from aqueous foams using astragalus membranaceus and attapulgite as stabilizer for efficient removal of cationic dyes

The water-based foam stabilized by the natural surfactant applied in the fabrication of porous materials has attracted extensive attention, as the advantages of cleanness, convenience and low cost. Particularly, the development of a green preparation method has became the main research focus and frontier. In this work, a green liquid foam with high stability was prepared by synergistic stabilization of natural plant astragalus membranaceus (AMS) and attapulgite (APT), and then a novel porous material with sufficient hierarchical pore structure was templated from the foam via a simple free radical polymerization of acrylamide (AM). The characterization results revealed that the amphiphilic molecules from AMS adsorbed onto the water-air interface and formed a protective shell to prevent the bubble breakup, and APT gathered in the plateau border and formed a three-dimensional network structure, which greatly slowed down the drainage rate. The porous material polyacrylamide/astragalus membranaceus/attapulgite (PAM/AMS/APT) showed the excellent adsorption performance for cationic dyes of Methyl Violet (MV) and Methylene Blue (MB) in water, and the maximum adsorption capacity could reach to 709.13 and 703.30 mg/g, respectively. Furthermore, the polymer material enabled to regenerate and cycle via a convenient calcination process, and the adsorption capacity was still higher than 200 mg/g after five cycles. In short, this research provided a new idea for the green preparation of porous materials and the treatment of water pollution.

Sunlight-driven environmental photodegradation of 2-chlorobiphenyl (PCB-1) in surface waters: kinetic study and mathematical simulations

Polychlorinated biphenyls (PCBs) are a family of highly toxic, resistant, and persistent organic pollutants, among which 2-chlorobiphenyl (PCB-1) is one of the simplest. Most studies on PCBs' photochemistry are limited to their direct photolysis, while the important role of reactive photo-induced species (RPS) (hydroxyl radicals, HO●; singlet oxygen, 1O2; and triplet excited states of chromophoric dissolved organic matter, 3CDOM*) in removing PCBs in natural waters through indirect photolysis has not yet been evaluated. In this work, the rate constants of the reactions between aqueous PCB-1 and RPS were obtained under simulated solar radiation (450-W Xenon lamp and an AM 1.5 global filter) by competition kinetics, and the effects of the initial pollutant concentration and the physicochemical characteristics of the water were investigated. The direct photolysis quantum yield of PCB-1 in the range 290-800 nm was found as 1.60 × 10-2 mol Einstein-1. The value of kPCB-1,HO● = (6.80 ± 0.09) × 109 L mol-1 s-1 is in good agreement with the literature. For 1O2, kPCB-1,1O2 = (1.13 ± 0.20) × 106 L mol-1 s-1, while for 3CDOM*, kPCB-1,3CBBP* = (2.44 ± 0.04) × 109 L mol-1 s-1 and kPCB-1,3AQ2S* = (3.36 ± 0.04) × 109 L mol-1 s-1 were obtained using 4-benzoylbenzoic acid (CBBP) and anthraquinone-2-sulfonate (AQ2S) as CDOM proxies, respectively. These results show that the main pathways involved in PCB-1 photodegradation are the reactions with HO● and 3CDOM* together with direct photolysis. In addition, the photodegradation of PCB-1 in sunlit waters was simulated using the kinetic model APEX (Aqueous Photochemistry of Environmentally Occurring Xenobiotics). According to simulations, a greater influence of the water depth and dissolved organic carbon concentration (DOC) on the persistence of PCB-1 is expected, being only slightly influenced by the concentrations of nitrite, nitrate, and bicarbonate. Finally, based on data reported for Brazilian surface waters, the average half-life (t1/2) of PCB-1 is expected to vary from 2 to 14 days. In particular, the t1/2 in the Paranapanema River is estimated at 7 to 8 days.

Highly Efficient and Simultaneous Removal of Cr(VI) and Imidacloprid through a Ferrocene-Modified MIL-100(Fe) Composite from an Aqueous Solution

A novel nanocomposite [Fc-MIL-100(Fe)] was constructed by combining ferrocene (Fc) with the porous structural metal-organic framework [MIL-100(Fe)]. The proposed composite material could simultaneously and efficiently remove hexavalent chromium [Cr(VI)] and imidacloprid and reduced strongly noxious Cr(VI) to weakly noxious trivalent chromium [Cr(III)]. The removal efficiencies of the composite material for Cr(VI) and imidacloprid could reach 95% after 15 h. The adsorption process was determined by kinetics, isotherms, and thermodynamics. The results demonstrated that the adsorption kinetics of Cr(VI) followed the pseudo-second-order model mainly by chemisorption; meanwhile, the adsorption of imidacloprid by the material conformed to the pseudo-first-order kinetics, which indicated that physical adsorption was the main process. Additionally, the intraparticle diffusion model revealed that the uptake of imidacloprid and Cr(VI) occurred via intraparticle diffusion at the composite material. The adsorption procedure for Cr(VI) was fitted to the Langmuir model (R² = 0.995) via monolayer adsorption, and that for imidacloprid was fitted to the Freundlich model (R² = 0.995) due to multilayer or heterogeneous adsorption. The thermodynamic research confirmed that the adsorption procedure was exothermic and spontaneous. Infrared spectroscopy, X-ray photoelectron spectra, and the pH effect implied that intermolecular hydrogen bonding and electrostatic interaction played a crucial role during the removal process. Fc-MIL-100(Fe) also exhibited long-term stability and satisfactory regeneration and reusability. Therefore, this method may enhance an environmentally friendly and prospective approach for concurrently removing imidacloprid and Cr(VI) from wastewater.

Synthesis of Iron-Based Carbon Microspheres with Tobacco Waste Liquid and Waste Iron Residue for Cd(II) Removal from Water and Soil

Herein, a novel magnetic iron-based carbon microsphere was prepared by cohydrothermal treatment of tobacco waste liquid (TWL) and waste iron residue (WIR) to form WIR@TWL. After that, WIR@TWL was coated with sodium polyacrylate (S.P.) to fabricate WIR@TWL@SP, whose removal efficiency for bivalent cadmium (Cd(II)) was studied in water and soil. As a result, WIR@TWL@SP possessed a high Cd(II) removal efficiency, which could reach 98.5% within 2 h. The adsorption process was consistent with the pseudo-second-order kinetic model because of the higher value of adjusted R2 (0.99). The thermodynamic data showed that the adsorption process was spontaneous (ΔG° < 0) and exothermic (ΔH° = 32.42 KJ·mol-1 > 0). Cd(II) removal mechanisms also include cation exchange, electrostatic attraction, hydrogen-bond interaction, and cation-π interaction. Notably, pot experiments demonstrated that WIR@TWL@SP could effectively reduce Cd absorption by plants in water and soil. Thus, this study offers an effective method for remediating Cd(II)-contaminated water and soil and may have a practical application value.

Enzymatic hydrolysis lignin functionalized Ti3C2Tx nanosheets for effective removal of MB and Cu2+ ions

Functionalized two-dimensional Ti₃C₂T_x (TN-EHL) was prepared as an effective adsorbent for removal of methylene blue dye (MB) and copper ions (Cu²⁺). Enzymatic hydrolysis lignin (EHL), a reproducible natural resource, was used to functionalize the Ti₃C₂T_x nanosheets. EHL can not only introduce active functional groups into TN-EHL but also prevent the oxidation of Ti₃C₂T_x, thus promoting the adsorption performance of TN-EHL. The maximum adsorption capacities of TN-EHL50 (in which the EHL content is 50 wt%) for MB and Cu²⁺ were 293.7 mg g^-1 and 49.96 mg g^-1, respectively. The higher correlation coefficients (R²) of MB (0.9996) and Cu²⁺ (0.9995) indicating that their adsorption processes can be described by the pseudo-second-order kinetic model. The MB adsorption data fit the Freundlich isotherm with R² of 0.9953, whereas the Cu²⁺ ions adsorption data fit the Langmuir isotherm with R² of 0.9998. The thermodynamic analysis indicates that the adsorption process of MB and Cu²⁺ on TN-EHL50 is spontaneous and endothermic. Significantly, the Cu²⁺ ions were reduced to Cu₂O and CuO particles during the adsorption process. Therefore, TN-EHL has a great potential as an environmentally friendly adsorbent for MB removal and recovery of Cu²⁺ ions from wastewater.

Preparation of Honeycomb-Structured Activated Carbon-Zeolite Composites from Modified Fly Ash and the Adsorptive Removal of Pb(II)

In this paper, fly ash (FA) was successfully prepared into a honeycomb carbon-zeolite composite (CZC) with good adsorption and used for the removal of Pb(II) by a two-step method. Compared with general FA, the honeycomb structure of the CZC resulted in a ∼6× increase in the specific surface area, and the average pore size increased from 3.4 to 12.7 μm. The maximum adsorption capacity of CZCs for Pb(II) reached 185.68 mg/g in 40 min. The experimental data for the adsorption of Pb(II) by CZC showed that the results were in good agreement with the Langmuir adsorption model. The adsorbent prepared in this study has good application prospects in wastewater treatment and provides a new method for the resource recovery of FA.

Simple one-pot synthesis of manganese dioxide modified bamboo-derived biochar composite for uranium(VI) removal

Exploitation of bamboo-derived biochar offers a lucrative opportunity for using moso bamboo due to its short growth cycle, large quantity and universality. Novel MnO2 modified bamboo-derived biochar composites (MnO2@BBC) were...