Enhancement of selective adsorption of Cr species via modification of pine biomass

Assessment of carbonized himalayan chir pine biomass as an eco-friendly adsorbent for effective removal of industrial dyes

This study investigates the use of carbonized Himalayan Chir Pine Biomass, known as Chir Pine Activated Carbon (CPAC), as an eco-friendly and cost-effective adsorbent for efficient industrial dye removal, with a focus on environmental sustainability. By applying different additive treatments, four adsorbents (C1, C2, C3, and C4) were formulated. CPAC was synthesized through pyrolysis and characterized using various analytical techniques including FE-SEM, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The adsorption capacity of CPAC was evaluated using Malachite Green (MG) dye as a model contaminant. FE-SEM images revealed high porosity (~ 10 µm) and a high surface area (119.886 m2/g) as confirmed by BET testing. CPAC effectively removed MG dye within 30 min at a solution pH of 7. Langmuir and Freundlich isotherm models indicated both monolayer and multilayer adsorption, while kinetic models suggested chemisorption. The regeneration efficiency was assessed using 0.1 N HCl over five consecutive cycles, with C4 demonstrating a high regeneration tendency of 85% and only a 9% reduction in adsorption ability after the fifth cycle. The developed CPAC shows excellent potential for use in the textile, paper, and leather industries for industrial dye adsorption, contributing to the protection of aquatic ecosystems. Additionally, CPAC can be utilized in other water and air purification applications.

Thiol-functionalized black carbon as effective and economical materials for Cr(VI) removal: Simultaneous sorption and reduction

Hazardous Cr(VI) continues to pose critical concerns for environmental and public health, demanding the development of effective remediation methods. In this study, thiol-functionalized black carbon (S-BC) was proposed for Cr(VI) removal by mixing thioglycolic acid (TGA) with black carbon (BC) derived from rice straw residue at 80 °C for 8 h. Using a 1:40 (g mL-1) BC-to-TGA ratio, the resulting S-BC40 sample demonstrated significantly enhanced Cr(VI) sorption capacities of 201.23, 145.78, and 106.60 mg g-1 at pH 3.5, 5.5, and 7.5, surpassing its BC counterpart by 2.0, 2.3, and 2.2 times. Additionally, S-BC40 converted all sorbed Cr into Cr(III) species at pH ≥ 5.5, resulting in an equal distribution of Cr(OH)3 and organic Cr(III) complexes. However, approximately 13% of Cr sorbed on BC remained as Cr(VI) at pH 3.5 and 7.5. Both C-centered and S-centered thiyl radicals might contribute to Cr(VI) reduction; however, sufficient C-S groups replenished via thiol-functionalization was the key for the complete Cr(VI) reduction on S-BC samples as pH ≥ 5.5. Thanks to the exceptional Cr(VI) sorption capacity, affordability, and accessibility, thiol-functionalization stands out as a promising modification method for BC. It presents a distinct opportunity to concurrently achieve the objectives of efficient Cr(VI) remediation and waste recycling.

Antibacterial, antioxidant, Cr(VI) adsorption and dye adsorption effects of biochar-based silver nanoparticles‑sodium alginate-tannic acid composite gel beads

Ultrasonic extraction of Osmanthus fragrans was used for reducing Ag+ to prepare AgNPs, which were further loaded on barley distiller's grains shell biochar. By supplementary of sodium alginate and tannic acid, composite gel beads were prepared. The physical properties of biochar-based AgNPs‑sodium alginate-tannic acid composite gel beads (C-Ag/SA/TA) were characterized. SEM, FTIR, and XRD showed that biochar-based AgNPs were compatible with sodium alginate-tannic acid. CAg greatly improved the dissolution, swelling, and expansion of gel beads. Through the analysis by the agar diffusion method, C-Ag/SA/TA gel beads had high antibacterial activity (inhibition zone: 22 mm against Escherichia coli and 20 mm against Staphylococcus aureus). It was observed that C-Ag/SA/TA composite gel beads had high antioxidant capacity and the free radical scavenging rate reached 89.0 %. The dye adsorption performance of gel beads was studied by establishing a kinetic model. The maximum adsorption capacities of C-Ag/SA/TA gel beads for methylene blue and Congo red were 166.57 and 318.06 mg/g, respectively. The removal rate of Cr(VI) reached 96.4 %. These results indicated that the prepared composite gel beads had a high adsorption capacity for dyes and metal ions. Overall, C-Ag/SA/TA composite gel beads were biocompatible and had potential applications in environmental pollution treatment.

Surfactant supported chitosan for efficient removal of Cr(VI) and anionic food stuff dyes from aquatic solutions

In order to develop a novel and cost-effective adsorbent with outstanding adsorption capacity and excellent recyclability for anionic pollutants, the chitosan-modified cetyltrimethylammonium bromide sorbent (CS@CTAB) was fabricated. Fourier-transform infrared spectroscopy, N2 adsorption-desorption isotherm, elemental analysis, Thermogravimetric analysis, X-ray diffraction, and Scanning electron microscopy have been applied to evaluate both raw and surfactant modified chitosan (CS@CTAB). Azorubine, Sunset Yellow, and hexavalent chromium were used to study the adsorption behavior of CS@CTAB under various parameters such as adsorbent dose, initial dye and metal ion concentration, contact time, and temperature. Adsorption equilibrium, kinetics models and thermodynamic parameters were investigated. The adsorption isotherm fitted well with the Langmuir isotherm model, with a maximum adsorption capacity of 492.6 mg/g, 492.6 mg/g, and 490.196 mg/g for Azorubine, Sunset Yellow, and Hexavalent Chromium, respectively. The kinetic studies showed that the pseudo-second-order model provided a better correlation between experimental data. Furthermore, the calculated thermodynamic parameters confirmed that the adsorption of Cr(VI), E110, and E122 by CS@CTAB material is a spontaneous and exothermic process. The fabricated CS@CTAB adsorbent was employed for the efficient elimination of Azorubine, Sunset Yellow, and hexavalent chromium from real water samples, synthetic mixtures, and colored soft drinks, with a percentage of recovery of ~ 96%. The plausible adsorption mechanisms of Azorubine, Sunset Yellow, and hexavalent chromium on the surface of CS@CTAB are elucidated. The adsorption anticipated to be due to electrostatic interaction and hydrogen bond formation for hexavalent chromium; while the adsorption of Azorubine and Sunset Yellow, was assumed to be due to electrostatic interaction, hydrogen bonding, and n-π interaction. Finally, the study demonstrates the efficiency of CS@CTAB for the removal of anionic species from several samples, including natural water and colored beverages.

Cleanup of Cr(VI)-polluted groundwater using immobilized bacterial consortia via bioreduction mechanisms

Cr(VI) bioreduction has become a remedial alternative for Cr(VI)-polluted site cleanup. However, lack of appropriate Cr(VI)-bioreducing bacteria limit the field application of the in situ bioremediation process. In this study, two different immobilized Cr(VI)-bioreducing bacterial consortia using novel immobilization agents have been developed for Cr(VI)-polluted groundwater remediation: (1) granular activated carbon (GAC) + silica gel + Cr(VI)-bioreducing bacterial consortia (GSIB), and (2) GAC + sodium alginate (SA) + polyvinyl alcohol (PVA) + Cr(VI)-bioreducing bacterial consortia (GSPB). Moreover, two unique substrates [carbon-based agent (CBA) and emulsified polycolloid substrate (EPS)] were developed and used as the carbon sources for Cr(VI) bioreduction enhancement. The microbial diversity, dominant Cr-bioreducing bacteria, and changes of Cr(VI)-reducing genes (nsfA, yieF, and chrR) were analyzed to assess the effectiveness of Cr(VI) bioreduction. Approximately 99% of Cr(VI) could be bioreduced in microcosms with GSIB and CBA addition after 70 days of operation, which caused increased populations of total bacteria, nsfA, yieF, and chrR from 2.9 × 10⁸ to 2.1 × 10¹², 4.2 × 10⁴ to 6.3 × 10¹¹, 4.8 × 10⁴ to 2 × 10¹¹, and 6.9 × 10⁴ to 3.7 × 10⁷ gene copies/L. In microcosms with CBA and suspended bacteria addition (without bacterial immobilization), the Cr(VI) reduction efficiency dropped to 60.3%, indicating that immobilized Cr-bioreducing bacteria supplement could enhance Cr(VI) bioreduction. Supplement of GSPB led to a declined bacterial growth due to the cracking of the materials. The addition of GSIB and CBA could establish a reduced condition, which favored the growth of Cr(VI)-reducing bacteria. The Cr(VI) bioreduction efficiency could be significantly improved through adsorption and bioreduction mechanisms, and production of Cr(OH)₃ precipitates confirmed the occurrence of Cr(VI) reduction. The main Cr-bioreducing bacteria included Trichococcus, Escherichia-Shigella, and Lactobacillus. Results suggest that the developed GSIB bioremedial system could be applied to cleanup Cr(VI)-polluted groundwater effectively.

Asymmetric Alternative Current Electrochemical Method Coupled with Amidoxime-Functionalized Carbon Felt Electrode for Fast and Efficient Removal of Hexavalent Chromium from Wastewater

A large amount of Cr (VI)-polluted wastewater produced in electroplating, dyeing and tanning industries seriously threatens water ecological security and human health. Due to the lack of high-performance electrodes and the coulomb repulsion between hexavalent chromium anion and cathode, the traditional DC-mediated electrochemical remediation technology possesses low Cr (VI) removal efficiency. Herein, by modifying commercial carbon felt (O-CF) with amidoxime groups, amidoxime-functionalized carbon felt electrodes (Ami-CF) with high adsorption affinity for Cr (VI) were prepared. Based on Ami-CF, an electrochemical flow-through system powered by asymmetric AC was constructed. The mechanism and influencing factors of efficient removal of Cr (VI) contaminated wastewater by an asymmetric AC electrochemical method coupling Ami-CF were studied. Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) characterization results showed that Ami-CF was successfully and uniformly loaded with amidoxime functional groups, and the adsorption capacity of Cr (VI) was more than 100 times higher than that of O-CF. In particular, the Coulomb repulsion effect and the side reaction of electrolytic water splitting were inhibited by the high-frequency anode and cathode switching (asymmetric AC), the mass transfer rate of Cr (VI) from electrode solution was increased, the reduction efficiency of Cr (VI) to Cr (III) was significantly promoted and a highly efficient removal of Cr (VI) was achieved. Under optimal operating conditions (positive bias 1 V, negative bias 2.5 V, duty ratio 20%, frequency 400 Hz, solution pH = 2), the asymmetric AC electrochemistry based on Ami-CF can achieve fast (30 s) and efficient removal (>99.11%) for 0.5-100 mg·L^-1 Cr (VI) with a high flux of 300 L h^-1 m^-2. At the same time, the durability test verified the sustainability of the AC electrochemical method. For Cr (VI)-polluted wastewater with an initial concentration of 50 mg·L^-1, the effluent concentration could still reach drinking water grade (<0.05 mg·L^-1) after 10 cycling experiments. This study provides an innovative approach for the rapid, green and efficient removal of Cr (VI) containing wastewater at low and medium concentrations.

Amino-functionalization of lignocellulosic biopolymer to be used as a green and sustainable adsorbent for anionic contaminant removal

In this work, natural biopolymer stemming from lignocellulosic peanut hull biomass was used as a green and low-cost adsorbent to eliminate anionic Congo red (CR) and Cr(VI) ions from aqueous sample. In order to enhance the removal performance, the lignocellulosic biopolymer was subjected to amino-modification by the graft copolymerization of (3-acrylamidopropyl) trimethylammonium chloride and N, N'-methylenebisacrylamide. The property of the prepared amino-functionalized biopolymer (AFB) was examined through FTIR, TG, SEM, particle size analysis, zeta potential determination and XPS. The adsorption efficacy of AFB for CR and Cr(VI) was tested at different pH, contact time and initial concentration. The kinetic, isotherm and thermodynamics investigations revealed that the uptakes of CR and Cr(VI) were the combination processes of chemical and physical interactions, and both endothermic in nature. The AFB exhibited good reusability without significant loss in adsorption capacity after five consecutive cycles. Mechanistic analysis indicated that the quaternary ammonium groups in AFB contributed a lot to the binding of anionic compounds through electrostatic attraction. In addition, n-π and hydrogen bonding while reduction and coordination were also responsible for the removal of CR and Cr(VI), respectively. The present study provides a favorable strategy for the removal of anionic contaminates in water by using green and sustainable lignocellulosic wastes.

Insights into Cr(VI) removal mechanism in water by facile one-step pyrolysis prepared coal gangue-biochar composite

The acceleration of industrialization has increased the discharge of chromium-containing wastewater, posing serious threat to the eco-environment and human health. To remove Cr(VI) in wastewater and improve resource utilization of solid waste, coal gangue and rape straw were initially used to prepare coal gangue-rape straw biochar (CG-RS) composite. The effects of pyrolysis temperatures, solution pH, coexisting ions of Cr(VI) adsorption were investigated. Different adsorption models combined with site energy analysis were used to explore the adsorption behaviors and mechanisms. The results showed higher pyrolysis temperature (600 °C) prepared CG-RS had a larger adsorption capacity (9.2 mg/g) for Cr(VI) (pH = 5.0). Analysis of XPS indicated that CG-RS successfully loaded with Fe-O and Al-O functional groups, which mainly participated in the reduction of Cr(VI). Site energy analysis further proved that reduction and surface complexation were the main adsorption mechanisms. This study shows an effective removal of Cr(VI) by CG-RS, providing a new way for resource utilization of solid waste.

Green Nanoparticle-Aided Biosorption of Nickel Ions Using Four Dry Residual Biomasses: A Comparative Study

The green synthesis of titanium dioxide nanoparticles was performed using the sol-gel method for their use in the modification of several agricultural biomasses (orange, lemon, cassava and yam peels) to evaluate the enhancement of adsorption capacity. To this end, different particle sizes (0.355, 0.5 and 1.0 mm) and initial solution pHs (2, 4 and 6) were assessed to identify the optimum conditions for further experimentation with the selected lignocellulosic materials. The defined conditions reporting the highest removal yields were used to perform adsorption experiments for chemically modified biosorbents. The biomaterials were characterized via elemental and bromatological analysis in order to quantify their composition. After the incorporation of TiO2 nanoparticles, the resulting biosorbents were characterized via FT-IR and SEM techniques. The results revealed that the pH solution significantly affects the nickel ion uptake, reaching the best performance at pH = 6 for all biomasses. Unmodified biomasses shown adsorption capacities between 18–20 mg/g. For chemically modified with TiO2 orange peels and yam peels biomass, the increase in adsorption capacities was 21.3 and 18.01 mg/g, respectively. For cassava and lemon peels chemically modified, it was found the increasing in adsorption capacities with values of 21.3 and 18.01 mg/g, respectively, which suggested that the incorporation of nanoparticles enhances adsorption capacities.

Coffee Husk and Lignin Revalorization: Modification with Ag Nanoparticles for Heavy Metals Removal and Antifungal Assays

This study presents the use of the modified coffee husk and coffee lignin as sorbents in the heavy metal ions sorption of Pb(II), Cd(II), Cr(III), and Cu(II) in an aqueous solution. The modification of sorbents was carried out by the impregnation method, using silver nitrate (AgNO3) and sodium borohydride (NaBH4) as a nanoparticles’ (NPs) precursor, and reducing agent, respectively. The obtained nanocomposite material was morphologically characterized by electron microscopy. In addition, an evaluation of metal ions’ sorption, pseudo-first-order, and pseudo-second-order kinetics modeling was performed. Finally, antifungal activity was evaluated on different Candida species. Coffee and lignin modified with AgNPs increased the extraction capacity with the highest sorption for Pb ions with 2.56 mg/g and 1.44 mg/g, respectively.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Interaction behaviors of Cr(VI) at biotite-water interface in the presence of HA: Batch, XRD and XPS investigations

The interaction behaviors of heavy metals and micaceous minerals are extremely important to understand the environmental behaviors of heavy metals. In this work, the interaction behaviors of Cr(VI) and biotite in the presence and absence of HA were studied combining batch and spectroscopic approaches. Batch experiments showed that biotite had the ability to remove Cr(VI) from the water and the removal markedly increased with decreasing pH. However, sorption of total Cr onto biotite increased with increasing pH (2.0-4.0), whilst quickly decreased above pH ∼ 4.0. It was worth noting that redox process of Cr(VI) to Cr(III), caused by structural Fe(II) on biotite, was another important factor for the high removal of Cr(VI) in a pH range of 2.0-4.0. Ionic strength also influenced Cr(VI) removal that Cr(VI) removal became higher with increasing ion strength. The presence of HA did not show obvious macroscopic effect on Cr(VI) removal, however, HA could cover biotite surface, and promote the sorption of total Cr onto biotite and attenuate the reduction effect caused by Fe(II) on biotite. Spectroscopic approaches, like FT-IR, XRD and XPS further confirmed the existence of Cr(III) on biotite interacting with Cr(VI) and the reduction of Cr(VI) to Cr(III) was drove by the Fe(II) dissolving from biotite to Fe(III). Further, sorption effect and reduction effect competitively contributed to the Cr(VI) removal by biotite, and reduction effect played a more important role at lower pH.

Desorption of Coffee Pulp Used as an Adsorbent Material for Cr(III and VI) Ions in Synthetic Wastewater: A Preliminary Study

Some of the diverse agro-industrial waste generated in primary or secondary stages have proved to be promising biomaterials for treating aqueous effluents contaminated, in this case, with heavy metals. Therefore, it is necessary to know their optimal operating conditions and the regeneration or reusability of the solid by-product, an aspect related to desorption. Considering the above, this article presents the findings of a preliminary study related to the desorption process of coffee pulp without physicochemical modification (Castilla variety), an agricultural waste used as a sorbent of Cr(III and VI) ions in synthetic wastewater. The desorption efficiency of four eluting agents at defined concentrations (0.10M)-HC1, HNO₃, H₂SO₄, and EDTA-was evaluated in a time interval of 1 to 9 days. Likewise, the proposals for the sorption and/or desorption mechanisms proposed and reported in the literature with respect to the use of biosorbents derived from the coffee crop are presented. With respect to the results, the coffee pulp used in previous studies of the adsorption of chromium species mentioned (optimal conditions in synthetic water of particle size 180 μm, dose 20 g·L^-1, agitation 100 RPM, room temperature, time of 90 to 105 min) showed efficiencies in the removal of Cr(III) and Cr(VI) of 93.26% and 74.80%, respectively. Regarding the extracting substances used, H₂SO₄ 0.10 M was the one that presented the highest desorption percentage in both chromic species, with a desorption of 45.75% Cr(VI) and 66.84% Cr(III) in periods of 5 and 9 days, respectively, with agitation of 100 RPM and room temperature. Finally, the dissemination of preliminary results on the desorption of coffee pulp contaminated with chromic species without physicochemical modification is novel in this study, as similar work with this specific material has not yet been reported in the literature. On the other hand, the limitations of the study and future research are related to the evaluation at different concentrations and of other extractor solutions that allow improving the efficiency of desorption of these chemical species in a shorter time from the coffee pulp (with and without modification) as well as the reuse cycles. As a result, the desorption of coffee pulp used as an adsorbent material in real water could help researchers identify the possible interfering factors that affect the process (foreign anions and cations, organic matter, environmental conditions, among others).

Mitigating the Health Effects of Aqueous Cr(VI) with Iron-Modified Biochar

A large amount of chromium (Cr) has entered the natural environment from the wastewater and waste residues, and the hexavalent (Cr(VI)) is highly poisonous, threatening the ecological environment and human health directly. In this study, iron-modified biochar was prepared using honeysuckle residue as raw material and the ferric chloride impregnation method. Batch Cr(VI) adsorption experiments were carried out using the modified honeysuckle-derived biochar (MHDB) as an adsorbent. The results indicate that a pH of 2 was best for the adsorption removal of Cr(VI) in the initial pH range of 2-10. The adsorption kinetic data fitted the pseudo-second-order model best out of the two models, and the Langmuir model was better than the Freundlich model to describe the adsorption process. Thermodynamic analysis indicated that the adsorption process of Cr(VI) on MHDB had an endothermic and spontaneous nature, and the increasing temperature was conducive to the adsorption. The main mechanisms of Cr(VI) adsorption might be the physical adsorption (electrostatic interactions) and chemical adsorption (ion exchange, the reduction of Cr(VI) to Cr(III)). The efficient adsorption of Cr(VI) makes MHDB a potential material for Cr(VI)-containing wastewater treatment. This study provides a feasible adsorption material for mitigating the environmental hazards of chromium, which has a certain reference value for protecting environmental health.

Aquatic toxicity of particulate matter emitted by five electroplating processes in two marine microalgae species

Electroplating is a widely used group of industrial processes that make a metal coating on a solid substrate. Our previous research studied the concentrations, characteristics, and chemical composition of nano- and microparticles emitted during different electroplating processes. The objective of this study was to evaluate the environmental toxicity of particulate matter obtained from five different electrochemical processes. We collected airborne particle samples formed during aluminum cleaning, aluminum etching, chemical degreasing, nonferrous metals etching, and nickel plating. The toxicity of the particles was evaluated by the standard microalgae growth rate inhibition test. Additionally, we evaluated membrane potential and cell size changes in the microalgae H. akashiwo and P. purpureum exposed to the obtained suspensions of electroplating particles. The findings of this research demonstrate that the aquatic toxicity of electroplating emissions significantly varies between different industrial processes and mostly depends on particle chemical composition and solubility rather than the number of insoluble particles. The sample from an aluminum cleaning workshop was significantly more toxic for both microalgae species compared to the other samples and demonstrated dose and time-dependent toxicity. The samples obtained during chemical degreasing and nonferrous metals etching processes induced depolarization of microalgal cell membranes, demonstrated the potential of chronic toxicity, and stimulated the growth rate of microalgae after 72 h of exposure. Moreover, the sample from a nonferrous metals etching workshop revealed hormetic dose-response toxicity in H. akashiwo, which can lead to harmful algal blooms in the environment.