Removal of Cr6+ ions from water by electrosorption on modified activated carbon fibre felt

A novel magnetic adsorbent from activated carbon fiber and iron oxide nanoparticles for 2,4-D removal from aqueous medium

Carbonaceous materials have been widely applied as adsorbents, but there are some factors that affect their efficiency. In this context, advances in nanotechnology provide new and more efficient methodologies for water treatment. This study evaluated the efficiency of a novel carbon-based adsorbent developed from Brazilian polyacrylonitrile textile fiber and functionalized with iron oxide magnetic nanoparticles for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the aqueous medium. The synthesized adsorbent (ACF-Fe3O4) was characterized by FTIR, XRD, VSM, Zeta potential, SEM, EDX, and TEM. The characterization techniques showed that the adsorbent has peaks characteristic of its precursors and superparamagnetic characteristics, confirming the efficiency of the synthesis method. The adsorption tests evaluated the influence of adsorbent dosage, pH of the contaminant solution, contact time and temperature on the removal of 2,4-D. The experimental data were better adjusted by the pseudo-second order kinetic model and by the Langmuir isothermal model. The thermodynamic parameters revealed that the process is exothermic, spontaneous and thermodynamically favorable. Under the best experimental conditions, the maximum adsorption capacity obtained was 51.10 mg g-1 with an adsorbent concentration of 0.33 g L-1, natural pH of the solution, temperature of 288 K at the equilibrium time of six hours. Adsorbent reusage was studied in four desorption cycles. The adsorption mechanism can be explained through π-π bonds, hydrogen bonds and electrostatic interactions. The prepared material presented high-efficiency adsorption capacity of 2,4-D compared to other carbonaceous materials present in the literature, demonstrating its viability for the removal of this contaminant from the aqueous medium.

Carbonaceous adsorbents in the removal of aquaculture pollutants: A technical review of methods and mechanisms

Carbonaceous adsorbents (CAs) are becoming increasingly popular owing to their low-cost, ease of preparation, and versatility. Meanwhile, aquaculture is becoming a fundamental food industry, globally, due to a wide range of advantages such as economic and nutritional benefits, whilst protecting the depletion of natural resources. However, as with any farming, the technique is known to introduce a plethora of chemicals into the surrounding environment, including antibiotics, nutrients, fertilisers and more. Therefore, the treatment of aquaculture effluent is gaining traction to ensure the sustainable growth of the industry. Although the existing mitigation techniques are somewhat effective, they suffer from degradation of the water quality or harm to local environments/organisms. This article aims to identify the sources and impacts of various aquaculture pollutants. After which the authors will provide an environmentally friendly and novel approach to the treatment of aquaculture effluent using carbonaceous adsorbents. The article will detail discussions about the product life span, including, synthesis, activation, modification, applications in aqueous media, regeneration and End-of-Life (EoL) approaches, with a particular focus on the impacts of competitive adsorption between pollutants and environmental matrices. Some research gaps were also highlighted, such as the lack of literature applying real-world samples, the effects of competitive adsorption and the EoL applications and management for CAs.

Hydrophobicity Tuned Polymeric Redox Materials with Solution-Specific Electroactive Properties for Selective Electrochemical Metal Ion Recovery in Aqueous Environments

Adaptable redox-active materials hold great potential for electrochemically mediated separation processes via targeted molecular recognition and reduced energy requirements. This work presents molecularly tunable vinylferrocene metallopolymers (P(VFc-co-X)) with modifiable operating potentials, charge storage capacities, capacity retentions, and analyte affinities in various electrolyte environments based on the hydrophobicity of X. The styrene (St) co-monomer impedes hydrophobic anions from ferrocene access, providing P(VFc-co-St) with specific response capabilities for and greatly improved cyclabilities in hydrophilic anions. This adjustable electrochemical stability enables preferential chromium and rhenium oxyanion separation from both hydrophobic and hydrophilic electrolytes that significantly surpasses capacitive removal by an order of magnitude, with a robust perrhenate uptake capacity of 329 mg/g VFc competitive with established metal-organic framework physisorbents and 17-fold selectivity over 20-fold excess nitrate. Pairing P(VFc-co-X) with other solution-specific electroactive macromolecules such as the pH-dependent poly(hydroquinone) (PHQ) and the cesium-selective nickel hexacyanoferrate (NiHCF) generates dual-functionalized electrosorption cells. P(VFc-co-X)//PHQ offers optimizable energetics based on X and pH for a substantial 4.6-fold reduction from 0.21 to 0.04 kWh/mol rhenium in acidic versus near-neutral media, and P(VFc-co-St)//NiHCF facilitates simultaneous extraction of rhenium, chromium, and cesium ions. Proof-of-concept reversible perrhenate separation in flow further highlights such frameworks as promising approaches for next-generation water purification technologies.

Research Progress of Treatment Technology and Adsorption Materials for Removing Chromate in the Environment

Cr is used extensively in industry, so the number of Cr (VI) hazards is increasing. The effective control and removal of Cr (VI) from the environment are becoming an increasing research priority. In order to provide a more comprehensive description of the research progress of chromate adsorption materials, this paper summarizes the articles describing chromate adsorption in the past five years. It summarizes the adsorption principles, adsorbent types, and adsorption effects to provide methods and ideas to solve the chromate pollution problem further. After research, it is found that many adsorbents reduce adsorption when there is too much charge in the water. Besides, to ensure adsorption efficiency, there are problems with the formability of some materials, which impact recycling.

Innovative metal oxides (CaO, SrO, MgO) impregnated waste-derived activated carbon for biohydrogen purification

In this work, a series of innovative metal oxide impregnated waste-derived activated carbons (MO/AC) was synthesized and used to purify the simulated biohydrogen based on the concept of CO₂ removal from the gas stream. Effects of metal oxide types (CaO, SrO and MgO) and contents of the best metal oxides on the morphology and the CO₂ adsorption capacity from the biohydrogen were investigated. It was found that both metal oxide types and contents played an important role on the adsorbent textural property and surface chemistry as well as the CO₂ adsorption capacity. Among all synthesized adsorbent, the MgO-impregnated AC with 12 wt.% MgO (12MgO/AC) exhibited the highest CO₂ adsorption capacity of around 94.02 mg/g. With this successive adsorbent, the biohydrogen with the H₂ purity higher than 90 mol% can be achieved from the gas stream with 50 mol% CO₂ for the first 2 min of adsorption period in a fixed bed reactor. The mechanism of CO₂ adsorption occurred via a combined process of the physisorption and chemisorption. Besides, the 12MgO/AC exhibited a high recyclability after several repetitive adsorption/desorption cycles.

Capacitive deionization of high concentrations of hexavalent chromium using nickel-ferric-layered double hydroxide/molybdenum disulfide asymmetric electrode

To decontaminate wastewater affected by high concentrations of aqueous hexavalent chromium (Cr(VI)) and improve the capability of layered double hydroxide (LDH) as an electrode in the capacitive deionization (CDI) process, nickel-ferric-LDH (NiFe-LDH) and NiFe-LDH/molybdenum disulfide (NiFe/MoS₂) were synthesized using a hydrothermal method. Characterization results indicated that the flower-like cluster framework of MoS₂ was decorated with the NiFe-LDH. Addition of MoS₂ improved the conductivity, capacitance reversibility, charge efficiency, coulombic efficiency, and stability of NiFe/MoS₂. The CDI performance of aqueous Cr(VI) was evaluated using NiFe/MoS₂ and activated carbon as the anode and cathode, respectively. The process reached equilibrium within 240 min. The deionization capacity and removal ratio for Cr(VI) (100 mg/L, 100 mL) were 49.71 mg/g and 99.42 %, respectively, at 1.2 V and 20 mL/min. The isothermal data were accurately described using the Langmuir model, and the theoretical maximum deionization capacity of NiFe/MoS₂ for Cr(VI) was 106.2 mg/g. The interaction mechanisms included electrostatic attraction, surface complexation, and reduction. These findings indicate that NiFe/MoS₂ has feasible applications in practical wastewater treatment for Cr(VI) removal.

Valorization of spent disposable wooden chopstick as the CO2 adsorbent for a CO2/H2 mixed gas purification

A series of activated carbons (ACs) derived from spent disposable wooden chopsticks was prepared via steam activation and used to separate carbon dioxide (CO₂) from a CO₂/hydrogen (H₂) mixed gas at atmospheric pressure. A factorial design was employed to investigate the effects of the activation temperature and time as well as their interactions on the production yield of ACs and their CO₂ adsorption capacity. The activation temperature exhibited a much higher impact on both the production yield and the CO₂ adsorption capacity of ACs than the activation time. The interaction of both parameters did not significantly affect the yield of ACs, but did affect the CO₂ adsorption capacity. The optimal preparation condition provided ACs with a desirable yield of around 23.18% and a CO₂ adsorption capacity of 85.19 mg/g at 25 °C and 1 atm and consumed the total energy of 225.28 MJ/kg AC or 116.4 MJ/g-mol CO₂. A H₂ purity of greater than 96.8 mol% was achieved from a mixed gas with low CO₂ concentration (< 20 mol%) during the first 3 min of adsorption and likewise around 90 mol% from a mixed gas with a high CO₂ concentration (> 30 mol%) during the first 2 min. The CO₂ adsorption on the as-prepared ACs proceeded dominantly via multilayer physical adsorption and was affected by both the surface area and micropore volume of the ACs. The adsorption capacity was diminished by around 18% after six adsorption/desorption cycles. The regeneration of the as-prepared chopstick-derived ACs can be easily performed via heating at a low temperature and ambient pressure, suggesting their potential application in the temperature swing adsorption process.

Reuse solution of hardness industrial circulating cooling water: Targeted ion-selective electro-adsorption by functionalized electrode

A low-cost, efficient and environmentally friendly hardness ion selective electro-adsorption system for high-hardness industrial circulating cooling water reuse was constructed to simultaneously realize a high salt removal rate and hardness ion (Ca²⁺ and Mg²⁺) selection. Multiply modified graphite carbon felt (GCF) materials for both negative and positive electrodes were proposed simply and economically, and an electro-adsorption system for hardness control was assembled. The multiple modified GCF (GCF_M) materials were characterized by SEM, BET and FT-IR and the electrochemical performance was tested by CV and EIS; surface properties were studied by Zeta potential; the hardness ion removal selectivity and operational stability of the electro-adsorption system were tested. Hydrophilic functional groups were introduced in GCF_M electrode, GCF_M exhibited a large microporosity and demonstrated stable electrochemical performance in aqueous with a specific capacitance. The hardness ion selective electro-adsorption system achieved an adsorption capacity of 58.05 mg/g per circle for calcium ions and 31.03 mg/g for magnesium ions, indicating the superior hardness ion selectivity. In the circulating cooling water at the electro-adsorption stage, the ion removal performance was over 42.1% and maintain in good stability, GCF_M electrode showed excellent deionization performance and demonstrated the application potential of hardness ion selective electro-adsorption system.

Agricultural waste of sugarcane bagasse as efficient adsorbent for lead and nickel removal from untreated wastewater: Biosorption, equilibrium isotherms, kinetics and desorption studies

The aim of this study was to evaluate the removal of Pb (II) and Ni (II) from untreated waste water using sugarcane bagasse and possible desorption of the metal ions from the adsorbent for effective re-use. The effects of pH (4-6), temperature (30-70 °C), contact time (30-150 min) and adsorbent dosage (0.3-0.7 g) were examined. Optimum conditions for the removal efficiencies of Pb (89.31 %) and Ni (96.33 %) were pH, 6.0; temperature, 30 °C; contact time, 90 min. and adsorbent dosage, 0.5 g. The maximum monolayer adsorption capacities of Pb (II) and Ni (II) were 1.61 mg/g and 123.46 mg/g respectively, by fitting the equilibrium data to the Langmuir isotherm model. Freundlich isotherm and pseudo second order kinetic models were best fitted for Pb (II) and Ni (II) uptake. Desorption of the metal ions from the metal-loaded bagasse was best performed by HNO3 with removal efficiency of 85.2 %. Therefore, sugarcane bagasse has a high potential for removal of heavy metals from waste water and can be re-used at any time after desorption without losing its efficiency.

Facile filtration system to remove Diuron in aqueous solutions

Exposure to the herbicide Diuron may cause many undesirable effects on human health, leading to an increasing concern to preserve the quality of water intended for consumption. Therefore, the present study evaluated the removal of this contaminant in a gravitational filtration system, using different types of activated carbon fiber felt (ACFF) supported on the microfiltration membrane. The properties of the ACFF samples were investigated by X-Ray diffraction (XRD), Raman spectroscopy, Nitrogen adsorption assays, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and zeta potential analysis. The characterizations suggested that ACFF could be appropriate to remove Diuron in aqueous solutions. Among samples, the one denominated as ACFF-CO₂(200)H₂O showed the best performance during the permeation tests. In the first filtration cycle, the system took about 530 min to reach the saturation point (removal ceased), and 190 min for the second cycle. Along the process, the contaminant solution fluxes were higher than 100 L h^{- 1} m² and reached an average final removal of ~ 50%. These results were excellent, as the proposed treatment consists of a simple gravitational filtration system, easy to operate, and low-cost.

Removal of cadmium heavy metal ions from wastewater by electrosorption using modified activated carbon felt electrodes

Cadmium contamination in industrial wastewater is an environmental issue posing a great threat to human and animal life. However, the available methods for the removal of cadmium at lower concentrations are limited. Such processes are often accompanied by sludge formation and lead to heavy metal wastage. This paper focuses on the application of an electrosorption process using modified activated carbon felt (MACF) electrodes for the removal and recovery of lower concentration of cadmium from a simulated wastewater sample without sludge formation. Activated carbon felt (ACF) electrodes were treated with 20% HNO₃ for removing surface impurities and improving the surface area. The effect of the electrode modification was analyzed by performing various characterizations including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and cyclic voltammetry. The adsorption isotherm and kinetic models have also been studied. The effect of operating parameters including pH, voltage, initial concentration and time were analyzed and optimized using Box-Behnken design and were obtained as 6.42, 1.44 V, 0.50 mg/L and 131.51 min respectively. During the regeneration of electrodes, a concentrated cadmium solution of 18.55 mg/L was obtained, which showed the possibility of cadmium recovery. The maximum cadmium removal was 60.60% at the optimized conditions, revealing the significance of electrosorption for heavy metal treatment.

Triphenylamine Schiff base as a lipid droplet-targeted fluorescent probe using Si-O-Si as a bridge for the detection of Cr6+ applied in bio-imaging

Lipid droplets are known to play an important role in many cellular activities, as revealed by recent studies. Additionally, hexavalent chromium is considered extremely toxic because it readily passes through cellular membranes and easily accumulates in living cells. In this study, a novel lipid droplet-targeted fluorescent probe (Si-LDS) for recognition of Cr6+ in living cells was designed and synthesized using triphenylamine derivatives and organosiloxane. Si-LDS detected Cr6+ with high selectivity and sensitivity. The novel probe was successfully applied to cell imaging of exogenous Cr6+ in HeLa cells, and Si-LDS was able to localize mainly in the lipid droplets of HeLa cells. Si-LDS is the first lipid droplet-targeted fluorescent probe for monitoring Cr6+.