Effective adsorptive removal of dyes and heavy metal using graphene oxide based Pre-treated with NaOH / H2SO4 rubber seed shells synthetic graphite Precursor: Equilibrium Isotherm, kinetics and thermodynamic studies

Cloning and characterization of FMN-dependent azoreductases from textile industry effluent identified through metagenomic sequencing

Azo dyes, when released untreated in the environment, cause detrimental effects on flora and fauna. Azoreductases are enzymes capable of cleaving commercially used azo dyes, sometimes in less toxic by-products which can be further degraded via synergistic microbial cometabolism. In this study, azoreductases encoded by FMN1 and FMN2 genes were screened from metagenome shotgun sequences generated from the samples of textile dye industries' effluents, cloned, expressed, and evaluated for their azo dye decolorization efficacy. At pH 7 and 45°C temperature, both recombinant enzymes FMN1 and FMN2 were able to decolorize methyl red at 20 and 100 ppm concentrations, respectively. FMN2 was found to be more efficient in decolorization/degradation of methyl red than FMN1. This study offers valuable insights into the possible application of azoreductases to reduce the environmental damage caused by azo dyes, with the hope of contributing to sustainable and eco-friendly practices for the environment management. This enzymatic approach offers a promising solution for the bioremediation of textile industrial effluents. However, the study acknowledges the need for further process optimization to enhance the efficacy of these enzymes in large-scale applications.Implications: The study underscores the environmental hazards associated with untreated release of azo dyes into the environment and emphasizes the potential of azoreductases, specifically those encoded by FMN1 and FMN2 genes, to mitigate the detrimental effects. The study emphasizes the ongoing commitment to refining and advancing the enzymatic approach for the bioremediation of azo dye-containing effluents, marking a positive stride toward more sustainable industrial practices.

Comparative analysis of the equilibrium, kinetics, and characterization of the mechanism of rapid adsorption of Congo red on nano-biosorbents based on agricultural waste in industrial effluents

This study aims to remove Congo red dye from industrial effluent using economical agriculturally-based nano-biosorbents like magnetic orange peel, peanut shells, and tea waste. The nano-biosorbents were characterized by various analytical techniques like SEM, FT-IR, BET and XRD. The highest adsorption capacity was obtained under the following ideal conditions: pH = 6 (orange peel and peanut shells), pH = 3 (tea waste), and dosages of nano-biosorbents with varying timeframes of 50 min for tea waste and peanut shells and 30 min for orange peel. The study found that tea waste had the highest removal rate of 94% due to its high porosity and responsible functional groups, followed by peanut shells at 83% and orange peel at 68%. The Langmuir isotherm model was found to be the most suitable, with R2 values of 0.99 for tea waste, 0.92 for orange peel, and 0.71 for peanut shells. On the other hand, a pseudo-second-order kinetic model was very feasible, showing an R2 value of 0.99 for tea waste, 0.98 for peanut shells and 0.97 for orange peel. The significance of the current study lies in its practical application, enabling efficient waste management and water purification, thereby preserving a clean and safe environment.

Biopolymer Meets Nanoclay: Rational Fabrication of Superb Adsorption Beads from Green Precursors for Efficient Capture of Pb(II) and Dyes

Renewable, green, and safe natural biopolymer-derived materials are highly desired for the purification of pollutants, but significantly improving their performance without the introduction of additional harmful chemicals remains a huge challenge. Based on the concept of "structure optimization design", environment-friendly composite beads (named SA/PASP/RE) with excellent adsorption performance and recyclability were rationally constructed through a green ionic crosslinking route, using the completely green biopolymer sodium alginate (SA), sodium salt of polyaspartic acid (PASP), and the natural nanoclay rectorite (RE) as starting materials. The nano-layered RE was embedded in the polymer matrix to prevent the polymer chain from becoming over-entangled so that more adsorption sites inside the polymer network were exposed, which effectively improved the mass transfer efficiency of the adsorbent and the removal rate of contaminants. The composite beads embedded with 0.6% RE showed high adsorption capacities of 211.78, 197.13, and 195.69 mg/g for Pb(II) and 643.00, 577.80, and 567.10 mg/g for methylene blue (MB) in Yellow River water, Yangtze River water, and tap water, respectively. And the beads embedded with 43% RE could efficiently adsorb Pb(II) and MB with high capacities of 187.78 mg/g and 586.46 mg/g, respectively. This study provides a new route to design and develop a green, cost-effective, and efficient adsorbent for the decontamination of wastewater.

A novel oyster shell biocomposite for the efficient adsorptive removal of cadmium and lead from aqueous solution: Synthesis, process optimization, modelling and mechanism studies

This study highlights the effectiveness of oyster shell biocomposite for the biosorption of Cd(II) and Pb(II) ions from an aqueous solution. The aim of this work was to modify a novel biocomposite derived from oyster shell for the adsorption of Cd(II) and Pb(II) ions from aqueous solution. The studied revealed the specific surface BET surface area was 9.1476 m2/g. The elemental dispersive x-ray analysis (EDS) indicated that C, O, Ag, Ca were the predominant elements on the surface of the biocomposite after which metals ions of Cd and Pb were noticed after adsorption. The Fourier transform Irradiation (FT-IR) revealed the presence of carboxyl and hydroxyl groups on the surface. The effect of process variables on the adsorption capacity of the modified biocomposite was examined using the central composite design (CCD) of the response surface methodology (RSM). The process variables which include pH, adsorbent dose, the initial concentration and temperature were the most effective parameters influencing the uptake capacity. The optimal process conditions of these parameters were found to be pH, 5.57, adsorbent dose, 2.53 g/L, initial concentration, 46.76 mg/L and temperature 28.48°C for the biosorption of Cd(II) and Pb(II) ions from aqueous solution at a desirability coefficient of 1. The analysis of variance (ANOVA) revealed a high coefficient of determination (R2 > 0.91) and low probability coefficients for the responses (P < 0.05) which indicated the validity and aptness of the model for the biosorption of the metal ions. Experimental isotherm data fitted better to the Langmuir model and the kinetic data fitted better to the pseudo-second-order model. Maximun Cd(II) and Pb(II) adsorption capacities of the oyster shell biocomposite were 97.54 and 78.99 mg/g respectively and was obtained at pH 5.56 and 28.48°C. This investigation has provided the possibility of the utilization of alternative biocomposite as a sustainable approach for the biosorption of heavy metal ions from the wastewater stream.

Photocatalytic degradation of organic dyes using reduced graphene oxide (rGO)

Photocatalysts have developed into a successful strategy for degrading synthetic and organic toxins, such as chemicals and dyes, in wastewater. In this study, graphene oxide was reduced at different temperatures and used for degrading indigo carmine and neutral red dyes. The wide surface areas, strong adsorption sites, and oxygen functionalities of reduced graphene oxide (rGO) at 250 °C (rGO-250) produced more photocatalytic degradation efficiency and adsorption percentage. The catalyst dosage, initial dye concentration, solution pH and recyclability were all used to optimize the photocatalytic activity of rGO-250. This research presents a capable nano-adsorbent photocatalyst for the efficient degradation of organic dyes. GO and rGOs were also investigated for carbon dioxide (CO2) absorption properties. Results showed that rGO-250 has better CO2 adsorption properties than other rGOs. Overall, it was observed that rGO-250 has better photocatalytic and CO2 adsorption capabilities compared to graphene oxide reduced at different temperatures.

Biomass waste-derived carbon materials for sustainable remediation of polluted environment: A comprehensive review

In response to the growing global concern over environmental pollution, the exploration of sustainable and eco-friendly materials derived from biomass waste has gained significant traction. This comprehensive review seeks to provide a holistic perspective on the utilization of biomass waste as a renewable carbon source, offering insights into the production of environmentally benign and cost-effective carbon-based materials. These materials, including biochar, carbon nanotubes, and graphene, have shown immense promise in the remediation of polluted soils, industrial wastewater, and contaminated groundwater. The review commences by elucidating the intricate processes involved in the synthesis and functionalization of biomass-derived carbon materials, emphasizing their scalability and economic viability. With their distinctive structural attributes, such as high surface areas, porous architectures, and tunable surface functionalities, these materials emerge as versatile tools in addressing environmental challenges. One of the central themes explored in this review is the pivotal role that carbon materials play in adsorption processes, which represent a green and sustainable technology for the removal of a diverse array of pollutants. These encompass noxious organic compounds, heavy metals, and organic matter, encompassing pollutants found in soils, groundwater, and industrial wastewater. The discussion extends to the underlying mechanisms governing adsorption, shedding light on the efficacy and selectivity of carbon-based materials in different environmental contexts. Furthermore, this review delves into multifaceted considerations, spanning the spectrum from biomass and biowaste resources to the properties and applications of carbon materials. This holistic approach aims to equip researchers and practitioners with a comprehensive understanding of the synergistic utilization of these materials, ultimately facilitating effective and affordable strategies for combatting industrial wastewater pollution, soil contamination, and groundwater impurities.

Sugar molasses as a sustainable precursor for the synthesis of graphene sand composite adsorbent for tetracycline and methylene blue removal

Sugar molasses from agricultural waste could be a sustainable carbon source for the synthesis of graphene adsorbent introduced in this work. The sugar molasses was successfully converted to graphene-like material and subsequently coated on the sand as graphene sand composite (GSC), as proven by XRD, XPS, Raman spectroscopy, and SEM with EDX mapping analyses. The adsorption performance of GSC was evaluated against the removal of Tetracycline (TC) and methylene blue (MB) pollutants from an aqueous solution in a fixed bed column continuous-flow adsorption setup. The effect of different process conditions: bed height (4-12 cm), influent flow rate (3-7 mL/min), and contaminants' concentration (50-150 ppm) was investigated. The results revealed that column performance was improved by increasing the bed depth and lowering the flow rate and concentration of the pollutants. The best removal efficiency was obtained when the bed height was 12 cm, the influent flow rate of 3 mL/min, and the pollutants' initial concentration was 50 mg/L. Thomas, Adams-Bohart, and Yoon-Nelson models were attempted to fit the breakthrough curves. Regeneration of the GSC indicated the decline of breakthrough time from 240-280 to 180 min, reflecting the decrease in adsorptive sites due to the incomplete regeneration process. Overall, sugar molasses was shown to be a low-cost precursor for synthesizing valuable graphene material in the form of GSC, which can reduce the problem for industrial waste management of sugar molasses, and the GSC could be used as an adsorbent for environmental application.

Synthesis of highly fluorescent carbon quantum dots from rubber seed shells for the adsorption and photocatalytic degradation of dyes

The potentials of biomass-based carbon quantum dot (CQD) as an adsorbent for batch adsorption of dyes and its photocatalytic degradation capacity for dyes which are congo red (CR) and methylene blue (MB) have been conducted in this study. The CQDs properties, performance, behaviour, and photoluminescence characteristics were assessed using batch adsorption experiments which were carried out under operating conditions including, temperature, pH and dosage. The morphological analysis revealed that CQDs are highly porous, uniform, closely aligned and multi-layered. The presence of hydroxyl, carboxyl and carbonyl functional groups indicated the significance of the oxygenated functional groups. Spectral analysis of photoluminescence for CQDs confirmed their photoluminescent quality by exhibiting high excitation intensity and possessing greenish-blue fluorescence under UV radiation. The removal percentage of the dyes adsorbed for both CR and MB dyes was 77% and 75%. Langmuir isotherm and pseudo-second-order models closely fitted the adsorption results. Thermodynamics analysis indicated that the adsorption process was exothermic and spontaneous, with excellent reusability and stability. The degradation efficiency of CQDs on both dyes was more than 90% under sunlight irradiation and obeyed the first-order kinetic model. These results demonstrated CQDs to be an excellent adsorbent and outstanding photocatalyst for organic dye degradation.

A Critical Review of Snail Shell Material Modification for Applications in Wastewater Treatment

Sea material is becoming increasingly popular and widely used as an adsorbent in wastewater treatment. Snail shell, a low-cost and natural animal waste material, has been shown to have a high calcium content (>99%) and a large potential surface area for the development of sustainable adsorbents. This paper presents a novel synthesis of methods for using snail shell absorbent materials in the treatment of wastewater containing heavy metals, textile dyes, and other organic substances. Modified biochar made from snail shells has gained popularity in recent years due to its numerous benefits. This paper discusses and analyzes modification methods, including impregnating with supplements, combining other adsorbents, synthesis of hydroxyapatite, co-precipitation, and the sol-gel method. The analysis of factors influencing adsorption efficiency revealed that pH, contact time, temperature, initial concentration, and adsorbent dose all have a significant impact on the adsorption process. Future research directions are also discussed in this paper as a result of presenting challenges for current snail adsorbents.

Eco-Friendly Detoxification of Congo Red Dye from Water by Citric Acid Activated Bioadsorbents Consisting of Watermelon and Water Chestnuts Peels Collected from Indigenous Resources

The native peels of two cheap, locally available adsorbents, watermelon (PWM) and water chestnuts (PWC), were chemically processed with different chemicals as modifying agents for the determination and assessment of their adsorption ability for the removal and clearance of harmful, venomous, and pernicious Congo red (CGR), as an acidic nature anionic dye, from the aqueous system. In successive batch experiments, the citric acid-treated peels CPWM and CPWC have shown more promising adsorption performance than their raw and untreated peel counterparts due to the availability of additional adsorption active binding sites evidenced through FT-IR and SEM characterizations. In the Langmuir and Temkin models, the correlation coefficients ( $R^2$ ) for the adsorptive removal of CGR on CPWM, PWM, CPWC, and PWC are very close to unity, 0.99 for each case of adsorption performance. Furthermore, the $q_{\max }$ nonlinear statistical results for the elimination of CGR on citric acid-treated adsorbents (CPWM and CPWC) are 8.3 and 7.95 mg/g whereas for their unmodified forms (PWM and PWC) are 2.23 and 4.32 mg/g, respectively, reflecting homogenous and monolayer adsorption mechanism. The greater values of $B_T$ 1.4 and 1.3 J/mole, for adsorptive removal of dye on CPWM and CPWC, respectively, as compared to their unmodified forms PWM and PWC which are 0.53 and 0.55 J/mole, respectively, indicate the stronger adsorbate-adsorbent associations. The mechanism follows the pseudo second order in the better mode, while thermodynamic statics for ΔH0,ΔG0, ΔS0, and ΔE0, indicate spontaneous and exothermic behavior of adsorption. This study tends to suggest that citric acid-modified adsorbents CPWM and CPWC may indeed be exploited efficiently to eliminate Congo red dye from wastewater.

Biological Degradation of the Azo Dye Basic Orange 2 by Escherichia coli: A Sustainable and Ecofriendly Approach for the Treatment of Textile Wastewater

In this study, initially 11 different bacterial strains were tested for the degradation capabilities against Basic Orange 2 dye. In initial screening with 78.90% degradation activity, Escherichia coli emerged as the most promising strain to degrade the selected dye, and was then employed in subsequent experiments. For further enhancing the degradation capability of selected bacteria, the effects of various physicochemical parameters were also evaluated. Among the tested parameters, 20 ppm dye concentration, 1666 mg/L glucose concentration, a temperature of 40 °C, 666 mg/L sodium chloride concentration, pH 7, 1000 mg/L urea concentration, a 3-day incubation period and the use of sodium benzoate as a redox mediator (666 mg/L) were found to be ideal conditions to get the highest decolorization/degradation activities. Finally, all the mentioned parameters were combined in a single set of experiments, and the decolorization capacity of the bacteria was enhanced to 89.88%. The effect of pH, dye concentration, incubation time and temperature were found to be responsible for the optimum degradation of dye (p < 0.05), as predicted from the ANOVA (analysis of variance) of the response surface methodology. The metabolites were collected after completion of the process and characterized through Fourier transform irradiation (FTIR) and gas chromatography mass spectrometry (GC-MS). From the data obtained, a proposed mechanism was deduced where it was assumed that the azo bond of the dye was broken by the azoreductase enzyme of the bacteria, resulting in the formation of aniline and 3, 4-diaminobezeminium chloride. The aniline was then further converted to benzene by deamination by the action of the bacterial deaminase enzyme. The benzene ring, after subsequent methylation, was transformed into o-xylene, while 3, 4-diaminobezeminium chloride was converted to p-xylene by enzymatic action. These findings suggest that Escherichia coli is a capable strain to be used in the bioremediation of textile effluents containing azo dyes. However, the selected bacterial strain may need to be further investigated for other dyes as well.