CTAB-modified carboxymethyl cellulose/bagasse cryogels for the efficient removal of bisphenol A, methylene blue and Cr(VI) ions: Batch and column adsorption studies

Harnessing carboxymethyl cellulose and Moringa oleifera seed husks for sustainable treatment of a multi-metal real waste

This study aimed to evaluate effective treatment strategies for laboratory waste with an initial pH of 1.0, containing Cr6+, Mn2+, Co2+, Fe3+, Ni2+, Cu2+, Zn2+, Sr2+, Hg2+, and Pb2+ ions, focusing on flocculation, precipitation, and adsorption techniques. The study utilized microparticles derived from Moringa oleifera seed husks (MS), cryogels of carboxymethyl cellulose (CMC), and hybrid cryogels combining CMC and MS (CMC-MS25 and CMC-MS50) as adsorbents. The optimal strategy involved raising the pH to 7 using NH4OH, leading to the partial precipitation of metal ions. The remaining supernatant was then passed through columns packed with the aforementioned adsorbents. Utilizing CMC-MS25 and CMC-MS50 adsorbents resulted in the simultaneous removal of over 90% of the targeted metal ions. The adsorption of Cu2+ ions onto the adsorbents was facilitated by electrostatic interactions between Cu2+ ions and carboxylate groups, as well as Cu-OH chelation, as confirmed by X-ray photoelectron spectroscopy. Under optimized conditions, the fixed-bed column adsorption capacity was determined as 88.2 mg g-1. The CMC-MS25 adsorbents proved reusable at least 5 times, with the recovered Cu2+ ions potentially suitable for other processes. The scalability and feasibility of producing these novel adsorbents suggest a promising, cost-effective solution for treating complex matrices and recovering high-value metals, as copper.

Cellulose-based materials in environmental protection: A scientometric and visual analysis review

As sustainable materials, cellulose-based materials have attracted significant attention in the field of environmental protection, resulting in the publication of numerous academic papers. However, there is a scarcity of literature that involving scientometric analysis within this specific domain. This review aims to address this gap and highlight recent research in this field by utilizing scientometric analysis and a historical review. As a result, 21 highly cited articles and 10 mostly productive journals were selected out. The scientometric analysis reveals that recent studies were objectively clustered into five interconnected main themes: extraction of cellulose from raw materials and its degradation, adsorption of pollutants using cellulose-based materials, cellulose-acetate-based membrane materials, nanocellulose-based materials, and other cellulose-based materials such as carboxymethyl cellulose and bacterial cellulose for environmental protection. Analyzing the distribution of author keywords and thoroughly examining relevant literature, the research focuses within these five themes were summarized. In the future, the development of eco-friendly and cost-effective methods for extracting and preparing cellulose and its derivatives, particularly nanocellulose-based materials, remains an enduring pursuit. Additionally, machine learning techniques holds promise for the advancement and application of cellulose-based materials. Furthermore, there is potential to expand the research and application scope of cellulose-based materials for environmental protection.

Rapid and convenient synthesis of "green" ammonium-modified chitosan composite sponge with the existence of ascorbic acid for highly efficient removal of Congo red (CR)

In this study, a new green composite sponge made of chitosan and modified with ammonium ascorbate (ACS-CIT) was synthesized in just 10 min. Compared with CS-CIT (sponge prepared from acetic acid), ACS-CIT exhibits significantly enhanced adsorption performance for CR, with the saturated adsorption capacities increased from 353.667 to 1261.639 mg·g-1. The adsorption mechanism can be summarized as the generation of more hydrogen bonds, electrostatic attraction, and intra particle diffusion, revealing the addition of ascorbic acid introduced more hydroxyl groups, thereby enhancing the hydrogen bonding force, and the ammonium modification of chitosan improved the electrostatic attraction of the material, resulting in a significant increase in its adsorption capacity. Additionally, the prepared ACS-CIT showed excellent CR removal performance even in the presence of multiple interfering factors coexisting in the simulated wastewater, and the adsorption capacity remained stable after at least five cycles. Furthermore, the maximum bed capacity of ACS-CIT for CR is 1152.829 mg·g-1 under the given conditions of a flow rate of 1 mL·min-1, inlet concentration of 150 mg·L-1, a bed height of 1 cm respectively, and the breakthrough curve followed the Thomas model. The results indicated the eco-friendly and recyclable ACS-CIT is a promising adsorbent for CR dye removal in water.

Visualized adsorption and enhanced photocatalytic removal of Cr6+ by carbon dots-incorporated fluorescent nanocellulose aerogels

In this study, carbon dots (CDs) and titanate nanofibers (TNs) were mixed with TEMPO-oxidized nanocellulose (TOCNC) to prepare fluorescent nanocellulose aerogels (FNAs) by a Schiff base reaction. The resulting FNA can detect the adsorption of Cr6+ through the fluorescence quenching in CDs and promote the removal of Cr6+ through the synergistic effect of CDs in photocatalysis. The optimized FNA has a maximum adsorption capacity of 543.38 mg/g, higher than most reported Cr6+ adsorbents. This excellent performance is due to the porous structure of the aerogel, which gives it a high specific surface area of 20.53 m2/g and provides abundant adsorption sites. Simultaneously, CDs can enhance the amino-induced Cr6+ adsorption, improve the photocatalytic performance of TNs, and expose more adsorption sites through electrostatic adsorption of amino-induced reduction products (Cr3+). This study explores the preparation of visualized nanosorbents with enhanced photocatalytic removal of Cr6+ and provides a new direction for nanoscale photocatalysts.

Bisphenol A contamination in aquatic environments: a review of sources, environmental concerns, and microbial remediation

The production of polycarbonate, a high-performance transparent plastic, employs bisphenol A, which is a prominent endocrine-disrupting compound. Polycarbonates are frequently used in the manufacturing of food, bottles, storage containers for newborns, and beverage packaging materials. Global production of BPA in 2022 was estimated to be in the region of 10 million tonnes. About 65-70% of all bisphenol A is used to make polycarbonate plastics. Bisphenol A leaches from improperly disposed plastic items and enters the environment through wastewater from plastic-producing industries, contaminating, sediments, surface water, and ground water. The concentration BPA in industrial and domestic wastewater ranges from 16 to 1465 ng/L while in surface water it has been detected 170-3113 ng/L. Wastewater treatment can be highly effective at removing BPA, giving reductions of 91-98%. Regardless, the remaining 2-9% of BPA will continue through to the environment, with low levels of BPA commonly observed in surface water and sediment in the USA and Europe. The health effects of BPA have been the subject of prolonged public and scientific debate, with PubMed listing more than 17,000 scientific papers as of 2023. Bisphenol A poses environmental and health hazards in aquatic systems, affecting ecosystems and human health. While several studies have revealed its presence in aqueous streams, environmentally sound technologies should be explored for its removal from the contaminated environment. Concern is mostly related to its estrogen-like activity, although it can interact with other receptor systems as an endocrine-disrupting chemical. Present review article encompasses the updated information on sources, environmental concerns, and sustainable remediation techniques for bisphenol A removal from aquatic ecosystems, discussing gaps, constraints, and future research requirements.

Bacterial Cellulose Aerogels Derived from Pineapple Peel Waste for the Adsorption of Dyes

Valorization of pineapple peel waste is an attractive research topic because of the huge quantities of this byproduct generated from pineapple processing industries. In this study, the extract from pineapple waste was collected to produce a hydrogel-like form containing bacterial cellulose fibers with a three-dimensional structure and nanoscale diameter by the Acetobacter xylinum fermentation process. The bacterial cellulose suspension was subsequently activated by freeze-drying, affording lightweight aerogels as potential adsorbents in wastewater treatment, in particular the adsorptive removal of organic dyes. Intensive tests were carried out with the adsorption of methylene blue, a typical cationic dye, to investigate the influence of adsorption conditions (temperature, pH, initial dye concentration, time, and experiment scale) and aerogel-preparation parameters (grinding time and bacterial cellulose concentration). The bacterial cellulose-based aerogels exhibited high adsorption capacity not only for methylene blue but also for other cationic dyes, including malachite green, rhodamine B, and crystal violet (28-49 mg/g). However, its activity was limited for most of the anionic dyes, such as methyl orange, sunset yellow, and quinoline yellow, due to the repulsion of these anionic dyes with the aerogel surface, except for the case of congo red. It is also an anionic dye but has two amine groups providing a strong interaction with the hydroxyl group of the aerogel via hydrogen bonding. Indeed, the aerogel has a substantially large congo red-trapping capacity of 101 mg/g. Notably, the adsorption process exhibited similar performances, upscaling the solution volume to 50 times. The utilization of abundant agricultural waste in the simple aerogel preparation to produce a highly efficient and biodegradable adsorbent is the highlight of this work.

Green composite aerogel based on citrus peel/chitosan/bentonite for sustainable removal Cu(II) from water matrices

Here, we propose a green and sustainable 3D porous aerogel based on citrus peel (CP), chitosan (CS), and bentonite (BT). This aerogel is prepared through a simple sol-gel and freeze-drying process and is designed for efficient capture of Cu(II) ions from water matrices. CCBA-2, with its abundance of active binding sites, exhibits an impressive Cu(II) adsorption yield of 861.58 mg/g. The adsorption isotherm and kinetics follow the Freundlich and pseudo-second-order models, respectively. In the presence of coexisting mixed-metal ions, CCBA-2 demonstrates a significantly higher selectivity coefficient (KdCu = 1138.5) for removing Cu(II) ions compared to other toxic metal ions. Furthermore, the adsorption of Cu(II) ions by CCBA-2 is not significantly affected by coexisting cations/anions, ionic strength, organic matter, or different water matrices. Dynamic fixed-bed column experiments show that the adsorption capacity of Cu(II) ions reaches 377.4 mg/g, and the Yoon-Nelson model accurately describes the adsorption process and breakthrough curve. Through experiments, FTIR, and XPS analyses, we propose a reasonable binding mechanism between CCBA-2 and metal cations, involving electrostatic attraction and chemical chelation between Cu(II) and the functional groups of the aerogel. CCBA-2 saturated with Cu(II) ions can be successfully regenerated by elution with 1 M HNO3, with only a slight decrease in adsorption efficiency (5.3%) after 5 adsorption-desorption cycles. Therefore, CCBA-2 offers a cost-effective and environmentally friendly material that can be considered as a viable alternative for the green and efficient removal of toxic Cu(II) ions from wastewater.

Efficient recovery of bisphenol A from aqueous solution using K2CO3 activated carbon derived from starch-based polyurethane

Endocrine-disrupting compounds (EDCs) are increasingly polluting water, making it of practical value to develop novel desirable adsorbents for removing these pollutants from wastewater. Here, a simple cross-linking strategy combined with gentle chemical activation was demonstrated to prepare starch polyurethane-activated carbon (STPU-AC) for adsorbing BPA in water. The adsorbents were characterized by various techniques such as FTIR, XPS, Raman, BET, SEM, and zeta potential, and their adsorption properties were investigated comprehensively. Results show that STPU-AC possesses a large surface area (1862.55 m²·g^-1) and an abundance of functional groups, which exhibited superior adsorption capacity for BPA (543.4 mg·g^-1) and favorable regenerative abilities. The adsorption of BPA by STPU-AC follows a pseudo-second-order kinetic model and a Freundlich isotherm model. The effect of aqueous solution chemistry (pH and ionic strength) and the presence of other contaminants (phenol, heavy metals, and dyes) on BPA adsorption was also analyzed. Moreover, theoretical studies further demonstrate that hydroxyl oxygen and pyrrole nitrogen are the primary adsorption sites. We found that the efficient recovery of BPA was associated with pore filling, hydrogen-bonding interaction, hydrophobic effects, and π-π stacking. These findings demonstrate the promising practical application of STPU-AC and provide a basis for the rational design of starch-derived porous carbon.

Functionalized bioadhesion-enhanced carboxymethyl cellulose/polyvinyl alcohol hybrid hydrogels for chronic wound dressing applications

Wounds produced by trauma, burns, and chronic diseases cause millions of patients to suffer discomfort, pain, and, in many cases, disability and death, leading to enormous health, social and financial impacts globally. Regrettably, current clinical treatments for chronic wounds remain unsatisfactory. Thus, this study reports for the first time the design, development, and synthesis of chemically biofunctionalized hybrid hydrogels made of carboxymethyl cellulose (CMC) and poly(vinyl alcohol) (PVA) crosslinked by citric acid using an entirely biocompatible and green process. They demonstrated suitable physicochemical properties, cytocompatibility, and hemocompatibility to be applied as a smart wound dressing for skin tissue engineering. These novel hybrids were biofunctionalized with l-arginine and RGD peptide through carbodiimide mediated-amide formation to promote bioadhesion of fibroblast and keratinocyte cells as a potential enhancement for wound healing and skin tissue engineering applications.

Adsorption of Congo red dye in water by orange peel biochar modified with CTAB

In order to improve the adsorption effect of biochar on Congo red dye, this study used hexadecyl trimethyl ammonium bromide (CTAB) to organically modify orange peel biochar (OBC) to produce CTAB-modified orange peel biochar (NOBC), and the biochar before and after modification was analyzed by SEM-EDS, FTIR and BET. The adsorption performance of NOBC on Congo red dye was investigated and the adsorption mechanism was studied. The results showed that the adsorption amount was influenced by the initial concentration, adsorption time and solution pH. NOBC adsorbed 50 mg L^-1 CR with an equilibrium time of 60 min and an equilibrium amount of 290.1 mg g^-1, while the adsorption equilibrium time of OBC was 210 min and an equilibrium amount of 155.2 mg g^-1, the adsorption of CR by NOBC was above 210 mg g^-1 at pH 2 to 11, NOBC can be recycled three times. The experimental results showed that the adsorption data of CR on NOBC were consistent with the Langmuir isothermal adsorption model and the Pseudo-second-order model, and the mechanism of CR adsorption on NOBC mainly included electrostatic attraction and surface adsorption. In conclusion, NOBC is a promising material for dye wastewater adsorption.

Computer chip-inspired design of nanocellulose/carbon dots hydrogel as superior intensifier of nano-sized photocatalyst for effective Cr(VI) removal

Hydrogel, a common carrier of photocatalyst that suffers from compromised catalytic efficiency, is still far from practical application. Herein, based on "computer chip-inspired design", a novel nanocellulose/carbon dots hydrogel (NCH) was fabricated as superior intensifier instead of common carrier of sodium titanate nanofibre (STN), where carbon dots (CDs) enhanced amino group-induced adsorption for Cr(VI), promoted photocatalytic properties of STN via transferring the photogenerated electron-hole pairs and improved amino group-induced desorption for reduced product (Cr(III)) via electrostatic repulsion, showing an efficiency of 1 + 1 > 2. Adsorption and photocatalysis experiments demonstrated superior removal performance of the NCH incorporating STN, as shown by theoretical maximum adsorption capacity of 425.74 mg/g and kinetic constant of 0.0374 min^-1 in the photocatalytic process, which was nearly 6.6 and 7.3 times of STN. A series of experiments was conducted to confirm the novel mechanism of CDs-enhanced adsorption-photocatalysis-desorption synergy. This work not only provides new insights into the fabrication of a superior intensifier for nanosized photocatalyst, but also proposes one new mechanism of CDs-enhanced adsorption-photocatalysis-desorption synergy, which is helpful for designing and optimizing nanosized photocatalyst.

Polysaccharide-Based Composite Hydrogels as Sustainable Materials for Removal of Pollutants from Wastewater

Nowadays, pollution has become the main bottleneck towards sustainable technological development due to its detrimental implications in human and ecosystem health. Removal of pollutants from the surrounding environment is a hot research area worldwide; diverse technologies and materials are being continuously developed. To this end, bio-based composite hydrogels as sorbents have received extensive attention in recent years because of advantages such as high adsorptive capacity, controllable mechanical properties, cost effectiveness, and potential for upscaling in continuous flow installations. In this review, we aim to provide an up-to-date analysis of the literature on recent accomplishments in the design of polysaccharide-based composite hydrogels for removal of heavy metal ions, dyes, and oxyanions from wastewater. The correlation between the constituent polysaccharides (chitosan, cellulose, alginate, starch, pectin, pullulan, xanthan, salecan, etc.), engineered composition (presence of other organic and/or inorganic components), and sorption conditions on the removal performance of addressed pollutants will be carefully scrutinized. Particular attention will be paid to the sustainability aspects in the selected studies, particularly to composite selectivity and reusability, as well as to their use in fixed-bed columns and real wastewater applications.

Preparation and characterization of low-cost activated carbon from Moringa oleifera chemically activated using ZnCl2 for the adsorption of bisphenol A

The use of agricultural by-products such as Moringa oleifera plants is one effort to support the reduction of environmental pollution. Activated carbon produces from agricultural wastes is relatively less expensive and can replace traditional methods such as renewable as well as nonrenewable materials such as petroleum residue and coal. In this study, the removal of bisphenol A from aqueous media was studied using activated carbon produced from M. oleifera pods and peels. A batch adsorption study was carried out by varying the parameters of the adsorption process. A maximum removal percentage of 95.46% was achieved at optimum conditions of 2.5 g L^-1 adsorbent dose, pH 7, 60 min contact time and 20 mg L^-1 initial concentration of BPA. The BET surface areas of MOP, MOP-AC and MOP-ACZ were found to be 12.60, 4.10 and 45.96 m²/g, respectively. The experimental data were analyzed by Langmuir, Freundlich and Temkin adsorption isotherm models. Equilibrium data fitted well with the Langmuir isotherm with a maximum monolayer adsorption capacity of 20.14 mg g^-1. The rates of adsorption were found to conform to the pseudo-second-order kinetics with a good correlation. The results indicate that the M. oleifera activated carbon could be employed as a low-cost alternative to commercial activated carbon in the removal of BPA from water.

Potential of sugarcane bagasse in remediation of heavy metals: A review

Presence of heavy metal (HM) ions in wastewater have emerged as among the most prominent issues for improving water quality and reducing it's consequences for the environment, animal and public health. This paper mainly focuses on the remediation of HM ions from wastewater utilizing the relatively inexpensive and widely accessible agricultural waste-Sugarcane Bagasse (SCB). For this, a brief understanding of HMs was discussed (by understanding the sources and toxicity of HM, advantages and shortcomings of conventional processes). Apart from that, to understand the potential of SCB, this review would provide vital information on employing SCB biosorbent in natural and modified forms for HM removal. Therefore, various ways of SCB modifications (including physical, chemical, and composite formation), essential optimal operational conditions (solution pH, dosage of biosorbent, initial metal concentration, contact time, agitation speed, temperature, suitable isotherm and kinetic model) and involving adsorption mechanism were also studied. Finally, significant study gaps were identified to facilitate future research since SCB has been confirmed as a potential bio-adsorbent for removing HM ions.

Hydroxypropyl methylcellulose-sugarcane bagasse adsorbents for removal of 17α-ethinylestradiol from aqueous solution and freshwater

Adsorbents made of hydroxypropyl methylcellulose (HPMC) and sugarcane bagasse (BG) microparticles were applied for the separation of 17α-ethinylestradiol (EE2) from aqueous solution in batch, and from aqueous solution and freshwater in fixed-bed columns. HPMC chains and BG microparticles were crosslinked by the esterification with citric acid. The adsorbents presented compression modulus values that increased from 208 ± 20 kPa (pure HPMC) to 917 ± 90 kPa, when the content of BG particles added to HPMC was 50 wt% (HPMC50BG). The porosity (~ 97%), specific surface area (1.16 ± 0.10 m²/g) and swelling degree (20 ± 1 g water/g) values were not affected by the addition of BG particles. The adsorption isotherms determined for EE2 on HPMC and on HPMC50BG fitted to the Langmuir and Freundlich models; the adsorption capacity of HPMC was slightly higher than that of composite HPMC50BG. Nevertheless, the addition of BG particles rendered outstanding mechanical reinforcement and dimensional stability to the adsorbents. The adsorption was driven by (i) hydrophobic interactions between EE2 methylene and aromatic groups and HPMC methyl groups, as evidenced by FTIR spectroscopy, and (ii) H bonds between HPMC and EE2 hydroxyl groups, as revealed by the adsorption enthalpy change (ΔH_ads) of - 45 kJ/mol. Column adsorption experiments of EE2 from aqueous solution on HPMC and HPMC50BG indicated adsorptive capacity (q₀) values of 8.06 mg/g and 4.07 mg/g, respectively. These values decreased considerably for the adsorption of EE2 from river water, probably due to the competition of EE2 with humic substances dissolved in natural water. The HPMC adsorbents could be recycled retaining up to 83% of the original efficiency.

Fluorescent nanocellulose-based hydrogel incorporating titanate nanofibers for sorption and detection of Cr(VI)

Chromium pollution is a major environmental concern; thus, effective and multifunctional adsorbents for removing the Cr(VI) ion are urgently needed. A fluorescent nanocellulose-based hydrogel (FNH) incorporating titanate nanofibers (TNs) was developed for the sorption and detection of Cr(VI) ion. The chemical and physical structures of the hydrogels, as well as their sorption and detection properties, were studied. The predicted maximum adsorption capacity and the lowest detection limit of FNH were 648.4 mg/g and 0.039 μg/L, respectively. Furthermore, the sorption and detection mechanisms of FNH were discussed in detail. These results showed that the excellent sorption and detection might be mainly attributed to the three-dimensional (3D) porous structure constructed by TNs and cellulose nanocrystals modified with carbon dots, which improved the sorption ability and provided the rapid visual response to Cr(VI). Furthermore, cost analysis showed that FNH was cheaper than activated carbon in removing the Cr(VI) ion. This work established a facile technique in developing low-cost and multifunctional adsorbents.

Multifunctional Cellulose and Cellulose-Based (Nano) Composite Adsorbents

In recent years, faced with the improvement of environmental quality problems, cellulose and cellulose-based (nano) composites have attracted great attention as adsorbents. In this review article, we first report the recent progress of modification and functionalization of cellulose adsorbents. In addition, the adsorbents produced by the modification and functionalization of carboxymehyl cellulose are also introduced. Moreover, the cellulose-based (nano) composites as adsorbents are reviewed in detail. Finally, the development prospect of cellulose and cellulose-based (nano) composites is studied in the field of the environment. In this review article, a critical comment is given based on our knowledge. It is believed that these biomass adsorbents will play an increasingly important role in the field of the environment.

Efficiency of air-dried and freeze-dried alginate/xanthan beads in batch, recirculating and column adsorption processes

Alginate (Alg) beads are low-cost adsorbents used for wastewater remediation. In this work, alginate (Alg) and alginate/xanthan (Alg/XG) blend beads were synthesized by gelation method into calcium chloride and freeze-dried to improve the porosity. Their adsorption efficiency was tested for methylene blue (MB) dye in batch, recirculating and column adsorption systems. The blend beads were characterized using by SEM, FTIR-ATR and X-ray microcomputer tomography (Micro-CT) analyzes. Freeze-dried Alg and Alg/XG beads presented porosity of 46 ± 5% and 77 ± 3%, respectively. Adsorption isotherms of MB on freeze-dried Alg/XG beads indicated better adsorption capacity in comparison to the air-dried ones. Adsorption kinetics and breakthrough curves based on recirculating and vertical column adsorption processes of MB on freeze dried Alg/XG and air-dried Alg/XG beads indicated higher efficiency for the vertical column system packed with freeze dried Alg/XG beads. The removal efficiency of 91% MB by the freeze-dried Alg/XG beads in vertical column remained even after four consecutive adsorption-desorption cycles, disclosing these beads as potential systems for the wastewater treatment.