Sustainable Adsorbent Research Articles

Investigation of regeneratable biopolymer-based aerogels for heavy metal decontamination from water: Quantum chemical analysis and experimental investigation

Heavy metals pose a significant threat to human health and ecological security due to their high toxicity, mobility, and persistence in the environment. Herein, the synthesis of a novel cellulose nanofiber-based aerogel using non-toxic biopolymers such as sodium alginate and polyglutamic acid to eradicate lead, zinc, and copper from water is described. The physical characterisation and the adsorption performance of the aerogels were evaluated in both monolithic and bead configurations. The study revealed superior adsorption performance for the aerogel beads compared to the monolithic configuration. The aerogel beads achieved a maximum adsorption capacity of 171.7 mg/g, 100.0 mg/g, and 142.0 mg/g for lead, zinc, and copper respectively. The aerogel beads exhibited a higher specific surface area compared to the monolithic aerogels. The presence of functional groups including carboxyl, amino, and hydroxyl groups on the aerogels likely facilitated the adsorption through coordinate bond formation and electrostatic interactions. Density Functional Theory calculations supported the role of oxygen and nitrogen containing groups on the aerogel in capturing heavy metal ions. The aerogels displayed a remarkable regeneration ability and were reused 20 times, without any significant reduction in the adsorption performance indicating its potential as a sustainable adsorbent for heavy metals removal from water.

Epipremnum aureum-derived nano-iron as a sustainable adsorbent for enhanced remediation of lead and chromium

Epipremnum aureum-derived nano-iron as a sustainable adsorbent for enhanced remediation of lead and chromium

Disposable Waste Aluminium Pan Derived Pseudoboehmite Nanoparticles for Concurrent Removal of Fluoride and Arsenate from Aqueous Medium

AbstractThe co‐occurrence of fluoride and arsenate in groundwater is a growing global concern owing to their synergistic adverse effect on human health. Thus, development of materials capable of capturing fluoride and arsenate simultaneously from aqueous medium is of much need. Moreover, it is a matter of great research importance to develop sustainable adsorbents by recycling solid wastes. Keeping this in mind, herein a novel pseudoboehmite nanoparticles (PBN) were synthesized by chemical valorization of disposable waste aluminium pan for simultaneous removal of fluoride and arsenate in aqueous medium. The physicochemical properties of the material were confirmed using analytical techniques such as XRD, BET, FT‐IR, FESEM etc. Batch study confirms the maximum monolayer adsorption of 90.10 mg g−1 and 94.84 mg g−1 of fluoride and arsenate respectively, which shows comparable affinity of the material for both contaminants. The selectivity of the adsorbent towards fluoride and arsenate was further evaluated by set of kinetic experiments in both single‐ion and mixture‐ion environment. The synthesis of pseudoboehmite nanomaterial using disposal waste Al pan and its high efficacy for removal of fluoride and arsenic even in presence of competing anionic environments provide a new direction of waste management for sustainable remediation of groundwater contaminants.

Investigation of kinetics and thermodynamics of methylene blue dye adsorption using activated carbon derived from bamboo biomass

This research paper aimed to evaluate the potential of activated carbon (AC) made from non-torrefied and torrefied bamboo biochar samples for the purpose of adsorbing methylene blue solution. The process involved impregnating bamboo biochar with a 5 M potassium hydroxide (KOH) solution at a 1:4 ratio of biochar to KOH, followed by carbonization at 800 °C, 900 °C, and 1000 °C to produce activated carbon samples. The samples were then characterized using techniques such as XRD, FESEM-EDX, FTIR, FE-TEM, and BET analysis to study their respective phase, surface morphology, elemental composition, functional groups, and structural and surface properties. The results showed that the torrefied bamboo AC exhibited a specific surface area of 366 m2/g and a total pore volume of 0.24 m3/g. Kinetic analyses showed adsorption following a pseudo-second-order model, with a capacity of 83.3 mg/g according to the Langmuir model and a favorability constant of 0.52 from the Freundlich model. Thermodynamic studies revealed the process to be spontaneous and endothermic, with changes in enthalpy and entropy of 77,810.73 kJ/mol and 269.9 kJ/mol·K, respectively. These findings highlight the effectiveness of bamboo-derived AC as a sustainable adsorbent for MB dye removal, offering a promising solution for water pollution control.

Graphene oxide dots‐loaded chitin flask: A sustainable adsorbent for separating multiple dyes from water

AbstractThis research endeavors to comprehensively explore the sorption dynamics of dyes from aqueous solutions utilizing a graphene oxide‐chitin (GO‐chitin) biosorbent. The investigation systematically evaluates the influence of key parameters, including temperature, pH, duration of contact, and initial dye doses, on the sorption efficiency of the biosorbent. Results obtained indicated that at acidic pH range, the dye removal efficacy was more than 80% for methyl orange and Remazol Brilliant Blue. Maximum removal efficacy was achieved within the 30 min of adsorption studies. Notably, the study underscores the remarkable adsorption capacity of GO‐chitin, varies in the range of 75% and 95%, for all three dyes, positioning it as a highly promising material for the remediation of polluted aquatic environments. The adsorption follows pseudo‐second‐order kinetics and Freundlich isotherm. These findings contribute valuable insights into the potential application of GO‐chitin as an effective biosorbent in the context of wastewater treatment, emphasizing its role in addressing environmental challenges associated with dye contamination in aqueous systems.

Sustainable fabrication of a novel ZIF-67 modified with Atriplex halimus-mediated MoO3/GO-NH2 for expeditious removal of nitrophenol

Herein, a novel, green, and sustainable MoO3/ZIF-67/AmGO composite has been fabricated for the removal of notorious o-nitrophenols (o-NPs) from wastewater. Atriplex halimus L. (saltbush) served a dual function where the plant extract was used for the synthesis of molybdenum trioxide (MoO3) NPs, while the spent biomass-derived biochar was utilized as feedstock to produce green graphene oxide (GO). Ultimately, the MoO3/ZIF-67/AmGO composite was in situ fabricated by mixing MoO3 and AmGO with ZIF-67 during its preparation by the self-templating approach. Remarkably, the adsorption of o-NP onto MoO3/ZIF-67/AmGO attained equilibrium in just less than 10 min. The kinetics and isotherms analyses verified that the o-NP adsorption onto MoO3/ZIF-67/AmGO adhered to the Pseudo-2nd-order and Freundlich models, with a consistent qmax value of 500 mg/g. A conceivable adsorption mechanism was investigated in detail. Moreover, the ionic strength test implied the impact of the salting-out phenomenon in boosting o-NP adsorption. The eco-friendly MoO3/ZIF-67/AmGO proves to be a sustainable adsorbent, displaying excellent recyclability in consistently removing o-NP across multiple cycles.

Solid foam composite derived from cement and jujube core activated carbon: a sustainable adsorbent for textile wastewater treatment

The textile industry is responsible for a significant amount of environmental damage caused by the use of dyes, which puts the health of humans and the ecosystems in the surrounding area in dire danger. The conventional approaches to wastewater treatment can be rather expensive and demand a significant amount of energy. Regrettably, these techniques are not very efficient when it comes to dealing with the substantial quantities of coloured wastewater that are generated by the textile sector. The utilisation of cement-activated carbon solid foam composite technology is a viable option that offers significant advantages in terms of both efficiency and environmental impact. These solid foam adsorbents are produced by the utilisation of a manufacturing process that is environmentally friendly and ingredients that are sourced locally, such as jujube cores. Even at low initial dye concentrations, they had clearance rates of over 98%, which is an impressively high percentage from their dye retention capabilities. In order to demonstrate the composite's potential for use in wastewater treatment applications, characterization techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and EDX are utilised. After conducting in-depth research, it has been established that the mass of the adsorbent and the length of time that it is in contact with the substance have a significant impact on the removal efficiency. The most favourable conditions have been seen to occur within a time range of ninety minutes, according to those observations. Methylene blue can be effectively removed with the help of the solid foam Composite, which is a sorbent that is not only readily available but also practical, cost-effective, and readily available. According to the findings of equilibrium research, the Temkin isotherm model is the one that is most suitable for understanding the behaviour of adsorption. As an additional point of interest, desorption experiments have shown that there are strong bindings between the dye and the composite, which indicates that there is minimal reversibility.

Enhanced uranium removal from leach liquor using raw and activated sludge as sustainable adsorbents

ABSTRACT To eliminate uranium from sulphate leach solution, this study introduces an economical, environmentally friendly adsorbent derived from dewatered municipal sludge (RS) and activated (AS) using calcium oxide. Various analytical methods, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer – Emmett – Teller (BET) analysis, and X-ray fluorescence spectroscopy (XRF), were employed in the characterisation of both materials. The efficacy of these adsorbents in removing uranium from sulphate leach fluid was systematically explored resulting in the achievement of a maximum adsorption capacity of 33.0 mg g−1 and 60.2 mg g−1 for RS and AS respectively. These adsorption capacity were detected using the following operational parameters: solution pH equals 2.0, 240 min as a contact time between the adsorbent and U(VI) solution, U(VI) initial concentration of 250 mg L−1, adsorbent dosage of 5.0 g L−1 and room temperature. The pseudo-second order kinetic and Langmuir isotherm models were determined to be the most suitable for the U(VI) adsorption process, showing a chemisorption, monolayer, and uniform process for the uranium adsorption by both materials. Using 1.0 M hydrochloric acid, over 96% of the U(VI) was successfully desorbed from the loaded sorbent, and AS sorbent held its stability for six sorption/desorption cycles in a row. Overall, this study offers a promising solution for sewage sludge disposal while addressing economic and environmental concerns.

KOH-Activated Dragon Fruit Peels for Cd2+ Ions Adsorption from Water

This study investigates the potential of KOH-activated dragon fruit peels as an adsorbent for the removal of Cd2+ ions from solution. The adsorption performance of the activated dragon fruit peels was evaluated through batch adsorption experiments, where various parameters including adsorbent dosage, initial Cd2+ concentration, contact time, and solution pH were examined. The optimum condition for the adsorption process was pH 5, stirring time 120 min, adsorbent dosage of 20 mg (in 25 mL solution). The findings highlight the potential of utilizing agricultural waste materials, such as dragon fruit peel, as an effective and sustainable adsorbent for the removal of heavy metal ions from water sources, contributing to environmental remediation efforts.

Hydrothermal carbonization of biomass waste and application of produced hydrochar in organic pollutants removal

This novel research, presents the study of utilizing the wild almond shell as biomass waste to fabricate hydrochar using the hydrothermal carbonization (HTC) method based on a central composite design (CCD) with two independent variables (time and temperature) and three responses; productivity, higher heating value (HHV) and norfloxacin (NOR) adsorption capacity. The prepared hydrochar at 200 °C and 8 h was then employed to produce activated carbon (AC) by chemical-thermal activation technique. Hydrochar and AC were characterized using XRD, BET, SEM-EDX, Raman, and FTIR techniques. The pore development, resulting in a rise in the SBET (637.46 m2/g) value occurred after the activation process. Moreover, the results of XRD and Raman analyses revealed a decrease in graphitization degree. The adsorption of norfloxacin, methylene blue (MB), and sunset yellow (SY) by prepared hydrochar and AC were studied to assess the impact of the pH of the solution, initial concentration, temperature, and contact time. The maximum adsorption capacity for NOR, MB, and SY using hydrochar and AC were 85.37, 153.46, 93.35, and 384.1625, 556.465, 264.93 mg/g, respectively. The experimental data for the adsorption of NOR, MB, and SY using hydrochar and AC illustrated a good fit with the PSO model. Besides, the Langmuir and Freundlich models indicated better fitting with empirical data obtained for the adsorption of NOR, MB, and SY, respectively. Thermodynamic study outcomes validated the exothermicity and spontaneity of the adsorption process for both absorbents. This study presents a new opportunity to develop the circular economy by fabrication of sustainable adsorbents with high adsorption capacity for organic pollutants from biomass waste.

Cellulose-Based Waste in a Close Loop as an Adsorbent for Removing Dyes from Textile Industry Wastewater

In an attempt to reuse fibrous textile waste and, at the same time, to address dye pollution in textile wastewater, waste cotton-based yarn was utilized as a cheap and sustainable adsorbent, as well as a row material for carbon adsorbent production. Unmodified yarn and cotton-based carbon adsorbents were used as adsorbents for dye removal from water. Cotton and cotton/polyester yarn samples underwent thermal modification through carbonization followed by chemical activation with KOH. Various techniques, including scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, and surface charge determination, were employed to analyze the morphological and surface characteristics of the cotton-based adsorbents. Adsorption properties were evaluated by testing the removal of selected cationic and anionic dyes from water. The impact of temperature, initial pH and concentration of the dye solution, and contact time on adsorption were investigated, and experimentally obtained data were analyzed using theoretical models. While carbonization alone did not significantly enhance adsorption properties, activated samples exhibited high efficacy in removing both cationic and anionic dyes from water. Despite the negative influence of the polyester component in the carbon precursor on the efficiency of activated samples in removing methyl orange, the results indicated that activated cotton and cotton/polyester yarn could be used to prepare highly efficient adsorbents for the rapid removal of methylene blue from real wastewater samples.

Removal of ciprofloxacin and heavy metals from water by bentonite/activated carbon composite: Kinetic, isotherm, thermodynamic and breakthrough curve modeling studies

This study explores the potential of a new, cost-effective adsorbent for removing ciprofloxacin (CIP) and heavy metals (HMs) from wastewater. This adsorbent is a mesoporous activated carbon (AC) crafted from sugarcane bagasse modified with bentonite (SCBB). The prepared composite was characterized using FTIR, XRD, SEM, and BET techniques. Optimal adsorption conditions were determined, with initial concentrations set at 15 and 300 mg/L, adsorbent doses at 100 and 50 mg, temperatures at 25 and 45 °C, and pH levels at 6 for CIP and HMs, respectively, in batch experiments. Kinetics data confirmed that adsorption follows pseudo-first-order model, with intraparticle diffusion identified as the rate-determining step. Three-parameter models were superior in describing experimental data compared to two-parameter models, with the Sips isotherm model indicating multilayer adsorption beyond monolayer saturation. Hydrophobicity likely plays a key role in CIP adsorption, potentially complemented by hydrogen bonding, while HMs are adsorbed through ion exchange, complexation, and pore diffusion processes. Furthermore, SCBB exhibited excellent adsorption performance (≥90 %) even after ten regeneration cycles. The impact of various operating parameters, including bed depth, feed concentration, and flow rate, were optimized in fixed bed column. Breakthrough data fitting the Dose Response, Thomas, and Yoon-Nelson models yielded high coefficients of determination (R2 ≥ 0.98). The techno-economic analysis identified SCBB preparation ($0.31/kg) as the main cost factor, but still predicts profitability with a payback period of 0.88 years and a break-even point of 58.6 %. Overall, the developed SCBB composite demonstrates significant potential as an efficient, cost-effective, and sustainable adsorbent, with applicability for the treatment of industrial wastewater contaminated with CIP and HMs.

Titania-carbon amalgamated nickel and copper layered double hydroxide for dye removal and catalytic reduction of p-nitrophenol

An economical and environmentally beneficial route for removing acid red 1 dye (A.R.) is titania‑carbon amalgamated nickel and copper layered double hydroxide, which is an efficient, and sustainable adsorbent. The utilized composite adsorbent consisting of layered double hydroxide (LDH) films with Ni and Cu, as well as TiO2-C have been fabricated to remove acid red 1 and develop a sustainable environmentally friendly way to convert p-nitrophenol into p-aminophenol. Miscellaneous characterization approaches were employed to examine the morphology, structure, and surface area of the synthesized composites. This study used a batch adsorption approach, which involved adjusting several factors, including adsorbent dosage, pH, and effect of co-existing inorganic materials. XRD, and FTIR characterization before and after adsorption showed robustness of the structure of the nanocomposite. The XPS analysis of TiO2-C@NiLDH and TiO2-C@CuLDH following the adsorption of A.R. revealed that the dye's shielding effect on the metal ions was the primary factor influencing the adsorption, rather than the degradation of the dyes. Moreover, the utilized nanocomposites exhibited an efficient catalytic activity for the conversion of p-nitrophenol to p-aminophenol using a hydrogen donor. Our findings exhibit that the LDH/TiO2-C hybrid with Ni demonstrates great stability even after being reused six times, and the suggested reaction mechanism has been documented.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation.

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Hierarchical ZnO/ZnFe2O4 yolk-shell adsorbent as a promising material for phosphate recovery and adsorption of organic pollutants from the simulated wastewater

Mitigation of phosphate contamination is essential to preserve the health and integrity of the water ecosystem. Therefore, to prevent eutrophication and preserve water resources, it is essential to establish an effective and long-lasting phosphate removal process. Herein, a highly efficient and eco-friendly ZnO/ZnFe2O4 (ZZFO) yolk-shell microsphere was designed by the glycothermal method followed by calcination for phosphate removal and adsorption of Congo red (CR) organic dye aqueous solution. ZZFO demonstrated an outstanding Langmuir hypothetical optimum phosphate adsorption ability of 103.2 mg-P/g in batch phosphate adsorption studies. This value is 5.54 and 8 times higher than that of pristine ZnO and Fe2O3, respectively, and the adsorbent was readily removed with the use of an external magnetic field. The anions experiments showed that, except chlorine and fluoride ions, other regular anions have a slight influence on the phosphate adsorption process. The Langmuir and pseudo-second-order model showed excellent correlation constants. Moreover, ZZFO exhibited the capability to adsorb CR aqueous solution, which is a significant finding for aquatic remediation. Our experimental findings have significant implications for the fabrication of sustainable adsorbents for the treatment of wastewater.

Innovative Green Alginate-Cellulose Composite for Light Lanthanides: Experimental Design and Comprehensive Studies on Kinetics, Equilibrium, Thermodynamics, and Reusability.

Nowadays, there is a great interest in efficient adsorbent development due to the recent demand for lanthanides, which are widely used in high-tech technology. Alginates, owing to their natural occurrence, gel formation capability, and safety, could be promising feasible adsorbents for lanthanide removal. This study proposes the alginate-cellulose composite as an ecological, sustainable adsorbent for light lanthanide sorption. The structure, morphology, qualitative and quantitative compositions, average diameter, and pHpzc of the composite were discussed in great detail. Using the batch approach, sorption trials were performed to evaluate the metal sorption performance. The maximum lanthanide accumulation was attained at pH 5.0 and a dosage of 0.05 g. The uptake kinetics are successfully explained by the Ho and McKay model, whereas the equilibrium data is best represented by the Langmuir equation. The presence of Cl-, NO3 -, SO4 2-, Ni(II), and Co(II) did not have any impact on the adsorption capacity. In turn, the presence of Fe(III) ions led to a 15 % reduction in the adsorption. The lanthanide ions were eluted from the adsorbent following the treatment with 0.1 M HNO3. The adsorbent retained over 95 % of its initial adsorption capacity after 6 series of sorption/desorption studies.

Silk adsorbent for green and efficient removal of methylene blue from wastewater.

Silk, a naturally occurring proteinaceous biopolymer with remarkable adsorbent properties, has been employed in wastewater remediation. The sericin coating, functioning as a protective barrier and rendering fibres impervious to external chemical attacks and preventing their involvement in chemical reactions, was removed using a greener alternative to harness silk as an effective adsorbent. Subsequently, the silk fibres underwent intermittent microwave degumming to extract sericin, and the fibres were utilized for the adsorptive exclusion of the hazardous methylene blue (MB) dye. The comparative batch adsorption studies (kinetics and isotherm) between raw silk fibres and degummed fibres were performed to comprehend the role of degumming on fibre adsorption efficacy by varying operating conditions, including pH, time of contact, initial adsorbate and dosage of adsorbent. The paramount adsorption capacity of raw silk was observed to be 137.08mgg-1 and 179.14mgg-1 for degummed silk when adsorbate conc. was 100ppm. The kinetics of adsorption obeyed pseudo-second order suggesting that the rate controlling step is chemisorptions, and data demonstrated greatest fit to Langmuir isotherm exhibiting mono-layer adsorption. Further, biodegradability was studied by mimicking natural environmental conditions where the raw and degummed silk fibres demonstrated 51% and 53% degradation, respectively, after 180days. Overall, based on obtained results, this study highlights the suitability of silk as an effective as well as sustainable adsorbent for the exclusion of toxic methylene blue dye from wastewater.

A novel green synthesis of MnO2-Coal composite for rapid removal of silver and lead from wastewater

The presence of Ag(I) and Pb(II) ions in wastewater poses a significant threat to human health in contemporary times. This study aims to explore the development of a novel and economical adsorbent by grafting MnO2 particles onto low-rank coal, providing an innovative solution for the remediation of water contaminated with silver and lead. The synthesized nanocomposites, referred to as MnO2-Coal, underwent thorough characterization using FTIR, XRD, BET, and SEM to highlight the feasibility of in-situ surface modification of coal with MnO2 nanoparticles. The adsorption of Ag(I) and Pb(II) from their respective aqueous solution onto MnO2-Coal was systematically investigated, with optimization of key parameters such as pH, temperature, initial concentration, contact time, ionic strength, and competing ions. Remarkably adsorption equilibrium was achieved within a 10 min, resulting in impressive removal rates of 80–90 % for both Ag(I) and Pb(II) at pH 6. The experimental data were evaluated using Langmuir, Freundlich, and Temkin isotherm models. The Langmuir isotherm model proved to be more accurate in representing the adsorption of Ag(I) and Pb(II) ions onto MnO2-Coal, exhibiting high regression coefficients (R2 = 0.99) and maximum adsorption capacities of 93.57 and 61.98 mg/g, along with partition coefficients of 4.53 and 71.92 L/g for Ag(I) and Pb(II), respectively, at 293 K. Kinetic assessments employing PFO, PSO, Elovich, and IPD models indicated that the PFO and PSO models were most suitable for adsorption mechanism of Pb(II) and Ag(I) on MnO2-Coal composites, respectively. Moreover, thermodynamic evaluation revealed the spontaneous and endothermic adsorption process for Ag(I), while exothermic behavior for adsorption of Pb(II). Importantly, this approach not only demonstrates cost-effectiveness but also environmental friendliness in treating heavy metal-contamination in water. The research suggests the potential of MnO2-Coal composites as efficient and sustainable adsorbents for water purification applications.

Cadmium removal efficiency from synthetic wastewater using sawdust as a sustainable adsorbent

Adsorption is one of the method that can be used to remove heavy metals from polluted water. Many adsorbents are naturally available and showed high performance in removing various pollutants. This study aimed to evaluate the performance of sawdust as a natural adsorbent agent to remove Cd ions from simulated wastewater and, also, to assess the improvement of sawdust adsorption capacity after activation by sulfuric acid (H2SO4). Many factors such as pH, contact time, temperature, and weight of the adsorbent were investigated in this study to evaluate their effect on the adsorption process. The results indicated a significant improvement of sawdust after modification (95.51% removal) compared to raw sawdust (82.22% removal). Equilibrium adsorption isotherms and kinetic study have been also carried out. Compared to the Langmuir adsorption isotherm model, the Freundlich isotherm model was best represented the experimental data of the sawdust. The experimental results of this sorbent were suitable for a pseudo-second order kinetic model. Moreover, the result pointed out that the process of adsorption was an endothermic and increasing the temperature resulted in a higher removal rate. Additionally, FTIR results revealed that the groups of carboxyl and hydroxyl contributed to the metal ions' ability to bind to surfaces. Finally, images of the surface structure of the sawdust before and after modification were obtained by using scanning electron microscopy (SEM) to analyze the surface morphology of both raw and treated sawdust.

Application of Corn Straw, an Agro-Waste, to Remove Dyes in an Aqueous Medium, Producing Blue or Red Fibers

The contaminant dyes that, even at low concentrations, may cause a series of adverse effects in humans and animals, and their removal by adsorption methods using alternative adsorbents as natural fibers, are regarded as a research topic that has become increasingly relevant. In this study, corn straw (CS), an agro-industrial residue, was used to remove dyes. The samples were characterized by ATR-FTIR, SEM-EDS, zeta potential, diffuse spectra, and colorimetry, before and after dye removal. The analyses allowed us to differentiate the morphology of CS after the treatment’s fiber on the adsorbent surface. The zeta potential showed a negative surface charge, but the acidic or alkaline treatment affected the surface charge of the sample, influencing the adsorption of cationic or anionic dyes. Adsorption data presented an increased removal when alkaline treatment was applied for the methylene blue (MB; qmax = 16.7 mg g−1), and the acid treatment was more effective for the Congo red (CR; qmax = 2.13 mg g−1). After color stability tests, it was observed that the anionic dye CR was more easily desorbed due to the surface charge of the adsorbent. Due to the chemical treatment, corn straw proved to be a good sustainable adsorbent for removing anionic or cationic dyes from aqueous media, contributing directly to the objective of sustainable development (#6—drinking water and sanitation) and with SDG numbers 3, 11, 12, 14, and 17.