Microwave assisted copolymerization of sodium alginate and dimethyl diallyl ammonium chloride as flocculant for dye removal

Emerging environmentally friendly bio-based nanocomposites for the efficient removal of dyes and micropollutants from wastewater by adsorption: a comprehensive review

Water scarcity will worsen due to population growth, urbanization, and climate change. Addressing this issue requires developing energy-efficient and cost-effective water purification technologies. One approach is to use biomass to make bio-based materials (BBMs) with valuable attributes. This aligns with the goal of environmental conservation and waste management. Furthermore, the use of biomass is advantageous because it is readily available, economical, and has minimal secondary environmental impact. Biomass materials are ideal for water purification because they are abundant and contain important functional groups like hydroxyl, carboxyl, and amino groups. Functional groups are important for modifying and absorbing contaminants in water. Single-sourced biomass has limitations such as weak mechanical strength, limited adsorption capacity, and chemical instability. Investing in research and development is crucial for the development of efficient methods to produce BBMs and establish suitable water purification application models. This review covers BBM production, modification, functionalization, and their applications in wastewater treatment. These applications include oil-water separation, membrane filtration, micropollutant removal, and organic pollutant elimination. This review explores the production processes and properties of BBMs from biopolymers, highlighting their potential for water treatment applications. Furthermore, this review discusses the future prospects and challenges of developing BBMs for water treatment and usage. Finally, this review highlights the importance of BBMs in solving water purification challenges and encourages innovative solutions in this field.

Dielectric barrier discharge plasma-modified chitosan flocculant and its flocculation performance

The flocculation performance of chitosan can be enhanced by grafting modification to overcome its disadvantages of poor water solubility. In this study, chitosan was modified by dielectric barrier discharge plasma and polymerized with acrylamide and aluminum chloride to synthesize a new chitosan-based flocculant, namely, chitosan-acrylamide-aluminum chloride (CA-PAC). After optimizing the synthesis conditions of CA-PAC, the best conditions were as follows: discharge time of 3 min, discharge power of 50 W, polymerization temperature of 60 °C, polymerization time of 3 h, total monomer concentration of 100 g/L, and m(AlCl3):m(CA) ratio of 2:1. Characterization was performed through SEM, XPS, FTIR, XRD, TG and 1H NMR. Results showed that the preparation of CA-PAC was successful. The influences of flocculant dosage, pH, and stirring intensity on flocculation efficiency were investigated. The removal efficiency of turbidity was 94.1 %. The investigation of the flocculation mechanism revealed that CA-PAC mainly relied on charge neutralization or the synergic action of electric neutralization, bridging, and roll-sweep under acidic and neutral conditions, but it depended on the joint action of adsorption bridging and net sweeping under alkaline conditions. This study provides new ideas for the preparation and development of modified chitosan and broadens its application in water treatment.

High performance, cost-effective and ecofriendly flocculant synthesized by grafting carboxymethyl cellulose and alginate with itaconic acid

Natural polymer flocculant possesses an exciting prospect in water treatment due to its non-toxicity, wide source, low cost and biodegradability. In this work, we have successfully synthesized the anionic terpolymer of carboxymethyl cellulose-itaconic acid‑sodium alginate (CIS) by microwave-assisted copolymerization. By studying the flocculation properties towards cationic dye of crystal violet (CV), the optimum synthesis conditions were determined. The maximum removal rate of 100 mg/L CV simulated wastewater was 92.2 % with CIS concentration of 30 mg/L. The flocculation kinetic results showed the rapid dye removal rate and the dye decolorization ratio of 89.8 % could be obtained at 75 s. Moreover, the CIS flocculant showed excellent flocculation effects in ambient pH of 4-10, flocculation temperature of 10-40 °C, and various inorganic salts. In general, the anionic CIS flocculant shows excellent cost effectiveness, where the predicted operation cost of as-prepared CIS is about 60 % of conventional polyacrylamide flocculant. It also has the advantages of excellent ecofriendliness and rich raw material source, indicative its potential applications of wastewater treatment.

Customized Utilization Strategies of Industrial Lignin to Produce Adsorbents and Flocculants Based on Fractionation and Adequate Structural Interpretation

Lignin, a by-product of pulping and biorefinery, has great potential to replace petrochemical resources for wastewater purification. However, the defects of lignin, such as severe heterogeneity, inferior reactivity and poor solubility, characterize the production process of lignin-based products by high energy consumption and serious pollution. In this study, several lignin fractions with relatively homogeneous structure were first obtained by organic solvent fractionation, and their structures were fully deciphered by various characterization techniques. Subsequently, each lignin component was custom-valued for wastewater purification based on their structural characteristics. Benefiting from the high reactivity and reaction accessibility, the lignin fraction (lignin-1) refined by dissolving in ethanol and n-butanol could been used as a raw material to produce cationic lignin-based flocculant (LBF) in a copolymerization system using green, cheap and recyclable ethanol as solvent. The lignin fraction (lignin-2) extracted by methanol and dioxane showed low reactivity and high carbon content, which was used to produce lignin-based activated carbon (LAC) with phosphoric acid as activator. Moreover, the influences of synthetic factors on the purification capacity were discussed, and the LBF and LAC produced under the optimal conditions showed distinguished purification effect on kaolin suspension and heavy metal wastewater, respectively. Furthermore, the corresponding purification mechanism and external factors were also elaborated. It is believed that this cleaner production strategy is helpful for the valorization of lignin in wastewater resources.

Simultaneous adsorption for cationic and anionic dyes using chitosan/electrospun sodium alginate nanofiber composite sponges

The coexistence of anionic and cationic dyes in dye wastewater has highlighted a great necessity to develop amphoteric adsorbents for their simultaneous removal. Herein, an amphoteric composite sponge was successfully fabricated by combining chitosan with electrospun sodium alginate nanofiber using lyophilization in acetic acid/water/dioxane mixed solvents, which owned the abundant functional groups and superior microstructure of interconnected pores and nanoscale fibers, beneficial for the adsorption capacity improvement. The optimum adsorption capacities for Acid Blue-113 and Rhodamine B were 926.2 ± 25.7 mg/g and 695.4 ± 17.0 mg/g, respectively, much higher than that of the controlled sample prepared with chitosan and non-spinning sodium alginate in traditional acetic acid/water solvents. Meanwhile, the sponge provided with the superior adsorption performance under various pH environment and cyclic adsorption. Importantly, it had considerable simultaneous adsorption capacity for binary system containing anionic and cationic dyes. Overall, the chitosan/electrospun sodium alginate nanofiber composite sponge shows potential for complex wastewater treatment.

Preparation of fibrous chitosan/sodium alginate composite foams for the adsorption of cationic and anionic dyes

Natural polysaccharide is attractive for preparing the environmentally friendly and highly efficient adsorbent. However, to obtain an efficient amphoteric absorbent for dealing with complex wastewater is still challenging. Herein, fibrous chitosan/sodium alginate composite foams were prepared by lyophilization with ternary acetic acid/water/tetrahydrofuran solvents, which had suitable morphology of interconnected pores and microscale fibers for dye adsorption. The amphoteric composite foams showed high adsorption capacities for both anionic Acid Black-172 (817.0 mg/g) and cationic Methylene Blue (1488.1 mg/g), which were far superior to those of the control samples prepared with traditional solvents of acetic acid/water. The adsorption kinetics and isotherm data showed that the adsorption followed the pseudo-second-order and Langmuir model. Further thermodynamics analysis revealed the adsorption was a spontaneous process. Meanwhile, the foams achieved effective adsorption capacity of AB-172 and MB dyes under a wide range of environmental pH, and maintained high adsorption efficiency even after four cycles. The adsorption mechanism is chemisorption, where the adsorption capacities for the anionic and cationic dyes were dependent on the mass ratio of chitosan to sodium alginate. As a novel amphoteric adsorbent, the fibrous chitosan/sodium alginate composite foam shows the potential to remove both cationic and anionic dyes from wastewaters.

Preparation of antistatic epoxy resin coatings based on double comb-like quaternary ammonium salt polymers

Two kinds of double comb-like quaternary ammonium salt polymers P(DPA-EPI) and P(DBA-EPI) with lower polarity were designed and synthesized using epichlorohydrin (EPI), di-n-propylamine (DPA) and di-n-butylamine (DBA) as raw materials. The transparent antistatic epoxy resin coatings were obtained using the two polymers as antistatic agents, respectively. Because P(DPA-EPI) and P(DBA-EPI) with good hygroscopic performance are easily dissolved in epoxy resin paints and are nearly linearly arranged in the epoxy resin paints, the obtained transparent antistatic epoxy resin coatings achieve good antistatic properties. The values of ρ_s of the coatings reach 5.13 × 10⁸ Ω sq⁻¹ and 2.69 × 10⁸ Ω sq⁻¹, respectively, with a lower addition amount of polymers of only 1.0 wt%. The two antistatic epoxy resin coatings also have good durability. Compared to the epoxy resin coating, with the introduction of P(DPA-EPI) and P(DBA-EPI), the thermal stability and adhesion of the antistatic epoxy resin coatings do not change obviously, but the Rockwell hardness values slightly reduce.

The antistatic epoxy resin coatings using double comb-like quaternary ammonium salt polymers as antistatic agents reach good antistatic property with lower addition amount because polymers can dissolve and nearly linearly arrange in the coatings.

Multistage reclamation of Co2+-containing alginate hydrogels as excellent reduction catalyst and subsequent microwave absorber by facile transformation

The multistage reclamation of materials has made contributions to sustainable development, but further progress is still sought after. In this work, functionalized seaweed-based composites were successfully prepared and utilized in multiple stages. Specifically, Co²⁺-containing alginate hydrogels (CHB-Co²⁺) prepared by sol-gel self-assembly and adsorption method using interior/exterior co-functionalized calcium alginate as raw materials were utilized for efficient reduction of p-nitrophenol. After coupling with freeze-drying and carbonization procedures, a high-performance Co/N co-doped carbonaceous microwave absorber was obtained and investigated in detail. By virtue of unique 3D interconnected network, heterogeneous interfaces and doped heteroatom N species, by which endowing the absorber with optimal impedance matching and attenuation ability, as-fabricated NC-Co-700 exhibited prominent microwave absorption performance with -54.2 dB of RL_min at 6.4 GHz and 5.3 GHz of maximum absorption bandwidth (from 12.7 to 18.0 GHz). Additionally, in view of the dielectric loss and magnetic loss caused by the synergy effect among the functional components, the underlying absorption mechanism was proposed. This work provided a novel idea for designing biomass-based functional materials and simultaneously achieved economic benefits through the rational utilization of other products in the preparation process.

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

Polymer flocculants are used to promote solid-liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.

Use of activated bentonite-alginate composite beads for efficient removal of toxic Cu2+ and Pb2+ ions from aquatic environment

The toxic heavy metals contamination in water bodies is one of the major concerns in many countries. Copper and lead are the two common toxic metals present in aquatic environments due to their extensive usage in various industries for diverse applications. The present study deals with the removal of these two toxic heavy metal ions using activated bentonite-alginate (ABn-AG) composite beads which are easily separated and recovered after adsorption reaction. Composite beads were prepared by adapting the ionic gelation method and the materials; i.e., raw bentonite (BnR), activated bentonite (ABn) and ABn-AG were characterized by XRD, BET surface area, TGA-DTA, FT-IR, SEM analyses. The nitrogen adsorption-desorption isotherm obtained for the materials were the type IV isotherm with characteristics H₃ hysteresis loops indicating the presence of mesopores with slit-shaped pores. Batch experiments showed that reasonably high percent removal was achieved even at highly acidic conditions, i.e., 58% of Cu²⁺and 77% of Pb²⁺were removed at pH 2.0. The removal was fast during the initial contact time and the adsorption data obtained at various contact time were fit well to the pseudo-second order kinetic model. The maximum sorption capacity for Cu²⁺ was found to be 17.30 mg/g whereas Pb²⁺ was found to be 107.52 mg/g. The presence of MgCl₂, NaCl and KCl did not cause significant influence on the removal of Cu²⁺ and Pb²⁺ using ABn-AG. Binary adsorption study suggested that Cu²⁺ and Pb²⁺ were removed through different binding sites present in ABn-AG. Reusability test showed that removal of Cu²⁺ and Pb²⁺ decreased by 10% only after the same material was reused for 5 times indicating that ABn-AG is a highly robust material and can be reuse for several times without losing its efficiency. Thus, this study suggested that ABn-AG composite beads can be employed as an efficient adsorbent for the removal of Cu²⁺ and Pb²⁺ from aqueous waste.