Efficient heavy metal removal from water by alginate-based porous nanocomposite hydrogels: The enhanced removal mechanism and influencing factor insight

Innovative biopolyelectrolytes-based technologies for wastewater treatment

Developing eco-friendly, cost-effective, and efficient methods for treating water pollutants has become paramount in recent years. Biopolyelectrolytes (BPEs), comprising natural polymers like chitosan, alginate, and cellulose, have emerged as versatile tools in this pursuit. This review offers a comprehensive exploration of the diverse roles of BPEs in combating water contamination, spanning coagulation-flocculation, adsorption, and filtration membrane techniques. With ionizable functional groups, BPEs exhibit promise in removing heavy metals, dyes, and various pollutants. Studies showcase the efficacy of chitosan, alginate, and pectin in achieving notable removal rates. BPEs efficiently adsorb heavy metal ions, dyes, and pesticides, leveraging robust adsorption capacity and exceptional mechanical properties. Furthermore, BPEs play a pivotal role in filtration membrane techniques, offering efficient separation systems with high removal rates and low energy consumption. Despite challenges related to production costs and property variability, their environmentally friendly, biodegradable, renewable, and recyclable nature positions BPEs as compelling candidates for sustainable water treatment technologies. This review delves deeper into BPEs' modification and integration with other materials; these natural polymers hold substantial promise in revolutionizing the landscape of water treatment technologies, offering eco-conscious solutions to address the pressing global issue of water pollution.

Remediate and sense: alginate beads empowered by portable electrochemical strips for copper ion removal and detection at environmental sites

The contamination of environmental sites due to the presence of persistent species represents an important issue to be tackled. In particular, the presence of high levels of metals in soil and surface water is more frequent. One of the metals that sometimes exceeds the permissible limit set by regulatory authorities is copper. For instance, copper-based fungicides are widely used in viticulture. However, copper ions remain in soil and can enter the food chain, posing threats to human health and environmental safety. Although the rapid detection of copper ions using portable sensors is effective in enhancing early warning, it sometimes solves only half of the problem as remediation is not considered. In this paper, we present a novel integrated/portable approach that merges the remediation and sensing of metals by proposing a remediate-and-sense concept. In order to realize this concept, alginate beads were coupled with printed electrochemical strips for on-site copper detection. Within the same architecture, alginate beads were used to remove copper ions from the soil, and printed electrochemical strips were used to evaluate the efficacy of remediation at the point of need. The concept was applied towards soil containing copper ions at the parts per billion level; with few alginate beads and in the absence of additional species, copper ions were quantitatively removed from the matrix; and 3D printing allowed us to combine the printed strips and spheres within a unique tool. The architecture was optimized and the results were compared to inductively coupled plasma-mass spectrometry (ICP-MS) measurements with a recovery percentage of 90%-110%. It should be noted that this novel portable approach may be applied to other pollutants, opening new possibilities for integrated remediation and sensing.

Biofilm hydrogel derived from physical crosslinking (self-assembly) of xanthan gum and chitosan for removing Cd2+, Ni2+, and Cu2+ from aqueous solution

This study aimed to fabricate a series of biodegradable hydrogel films by gelating/physically crosslinking a blend of xanthan gum (XG) and chitosan (CS) in various combinations using a facile, green, and low cost solution casting technique. The adsorption of Cd2+, Cu2+ and Ni2+ by the XG/CS biofilm in aqueous solution was studied in batch experiments to determine how the pH of the solution, contact time, dosage of adsorbent, initial metal ion concentration and ionic strength affect its adsorption. A highly pH-dependent adsorption process was observed for three metal ions. A maximum amount of Cd2+, Ni2+, and Cu2+ ions was adsorbable with 50 mg of the adsorbent at pH 6.0 for an initial metal concentration of 50 mg.L-1. An empirical pseudo-second-order model seems to fit the kinetic experimental data reasonably well. It was found that the Langmuir model correlated better with equilibrium isotherm when compared with the Freundlich model. For Cd2+, Ni2+, and Cu2+ ions at 25 °C, the maximum monolayer adsorption capacity was 152.33, 144.79, and 139.71 mg.g-1, respectively. Furthermore, the biofilm was capable of regenerating, allowing metal ions to adsorb and desorb for five consecutive cycles. Therefore, the developed biodegradable film offers the potential for remediation of specified metal ions.

Adsorptive removal of anthracene from water by biochar derived amphiphilic carbon dots decorated with chitosan

Anthracene belongs to the polycyclic aromatic hydrocarbon (PAH) consisting of benzene rings, unusually highly stable through more π-electrons and localized π-bond in entire rings. Aqueous-phase anthracene adsorption using carbon-based materials such as biochar is ineffective. In this paper, carbon dots (CDs) derived from the acid treatment of coconut shell biochar (CDs/MCSB) decorated with chitosan (CS) are successfully synthesized and applied for anthracene removal from aqueous solutions. The h-CDs/MCSB exhibited fast adsorption of anthracene with significant sorption capacity (Qmax = 49.26 mg g-1) with 95 % removal efficiency at 60 min. The study suggested chemisorption dominated monolayer anthracene adsorption onto h-CDs/MCSB, where a significant role was played by ion-exchange. Density Functional Theory (DFT) suggested the anthracene adsorption was dominated by the electrostatic interactions and delocalized electron, induced by higher polarizability of functional groups on the surface of hybrid CDs/MCSB assisted by chitosan (h-CDs/MCSB). In addition, the aromatic structure of CDs/MCSB and high polarizability of functional groups provided the strong interactions between benzene rings of anthracene and hybrid adsorbent-assisted multiple π-bond through delocalized π-bond and polarization-induced H-bond interactions. The presence of carboxylic and sulfonic groups on the CDs/MCSB surface also contributed to the effective adsorption of anthracene was confirmed by the fluorescence spectra. The results showed that the hybrid adsorbent was an effective material for removing PAHs, usually difficult to remove from water owing to the presence of benzene rings in their structures. Further, consistency in the DFT results suggested the outstanding binding capacity with the anthracene molecules with h-CDs/MCSB.

Selective removal of thallium from water by MnO2-doped magnetic beads: Performance and mechanism study

Aqueous thallium has posed an increasing threat to environment as human's intensified activities in mining, refining, process and discharge. Remediation on thallium pollution has been of up-most importance to water treatment. In present work, MnO2 and magnetic Fe3O4 have been implanted to sodium alginate (SA) in presence of carboxyl methyl cellulose (CMC), and the resultant beads consisted of SA/CMC/MnO2/Fe3O4 were characterized. The materials were applied to treatment of Tl-contaminated water as adsorbent in lab. The removal results revealed that the adsorption capacity reached 38.8 mg (Tl)·g (beads)-1 and almost 100 % removal efficiency was achieved. The residual Tl was below 0.1 μg·L-1, meeting the discharge standard regulated in China. The kinetic adsorption was better described as a pseudo-second-order and three-step intra-particle diffusion model. Freundlich isotherm was well fitted the experimental data. The absorbent shown an excellent competitive specificity (KTl/M: ∼104!) over common hazardous ions Cu2+, Cd2+, Co2+, Pb2+ and Cr3+, as well as naturally abundant K+ and Na+ (KTl/M: 10-102) in mimic environmental conditions. Regeneration and reusability of the absorbent was also verified by five absorption-desorpotion cycles. XPS results revealed that a redox reaction between Mn4+ with Tl+, and an ion exchange of H+ (-O-Fe) and Tl+ were assumed to be main process for the specific capturing. This study provided an efficient SA/CMC/MnO2/Fe3O4 composite beads that could be a promising adsorbent for Tl-polluted water treatment.

Superior reduction and immobilization of Cr(VI) in soil utilizing sulfide nanoscale zero-valent iron supported by phosphoric acid-modified biochar: Efficiency and mechanism investigation

A novel strategy was proposed to remediate Cr(VI)-contaminated soil via phosphoric acid-modified biochar supported sulfide nanoscale zero-valent iron (SnZVI@PBC). Results of characterizations revealed that FeSX shell existed in outer layer of nZVI to prevent its oxidation after sulfidation modification, and SnZVI was effectively dispersed owing to the support of PBC, accelerating the electron transport for Cr(VI) reduction. The SnZVI@PBC presented pH-dependence and fast capture for Cr(VI) with outstanding binding amount of 335.55 mg/g. More importantly, the Cr(VI) content declined from 1300.75 to 223.30 mg/kg with conversion into stable Cr(III) in soil after 42 d of remediation with 2.0 % SnZVI@PBC under 60 % moisture content. Furthermore, leaching experiments showed that SnZVI@PBC could effectively immobilize Cr(VI), decreasing its migration and harmful risks to plants and human. Particularly, the fractions of exchangeable and carbonate-bound Cr decreased by 96.77 % and 83.60 %, which transformed to relatively stable fractions. Interestingly, the presence of humic acid, and the freezing-thawing/wetting-drying process promoted the immobilization performance of SnZVI@PBC for Cr(VI). SnZVI@PBC could alleviate the migration and poisonousness of Cr(VI) in soil primarily via reduction, co-precipitation, pore filling, and electrostatic attraction. Overall, SnZVI@PBC could be considered as a feasible amendment with superior reducing capacity and immobilization performance for Cr(VI)-contaminated soil.

Drought-resistant and water-retaining tobermorite/starch composite hydrogel for the remediation of cadmium-contaminated soil

The objective of this work is utilizing fly ash to synthesize tobermorite (TOB) with a higher specific surface area and layered structure, and incorporating it into the starch/acrylic acid network to boost the drought resistance, water retention and heavy metal adsorption properties. The water absorption and water retention performance and cadmium adsorption characteristics of tobermorite/leftover rice-based composite hydrogel (TOB@LR-CH) were evaluated by water absorption swelling test, soil evaporation test and batch adsorption experiment. By adjusting the addition of TOB and other synthesized conditions, the swelling property (from 114.80 g/g to 322.64 g/g), water retention (71.80 %, 144 h) and Cd2+ adsorption characteristics (up to 591.36 mg/g) were significantly enhanced. Adding a moderate amount of TOB (2 wt%) provided the most uniform tobermorite dispersion during synthesis, and TOB2@LR-CH exhibited the most stable three-dimensional network and highest proportion of effective TOB. The adsorption behavior of cadmium on TOB2@LR-CH was more consistent with the pseudo-second-order kinetics and Langmuir isotherm models. Additionally, the regeneration test results displayed that the adsorption removal rate of cadmium by TOB2@LR-CH adsorbent remained stable after 5 cycles. This study demonstrates that TOB@LR-CH has good water absorption and water retention potential in arid and semi-arid soils, and also has potential application prospects in remediating Cd(II)-contaminated soil.

Current technologies for heavy metal removal from food and environmental resources

Exposure to heavy metals in water and food poses a significant threat to human well-being, necessitating the efficient removal of these contaminants. The process of urban development exacerbates heavy metal pollution, thereby increasing risks to both human health and ecosystems. Heavy metals have the capacity to enter the food chain, undergo bioaccumulation and magnify, ultimately resulting in adverse effects on human health. Therefore, implementing effective pollution control measures and adopting sustainable practices are crucial for mitigating exposure and associated health risks. Various innovative approaches, including adsorption, ion exchange, and electrochemical technology, are currently being actively investigated to cope with the issue of heavy metal contamination. These innovative methods offer benefits such as efficient recycling, cost-effectiveness and environmental friendliness. In this review, we summarize recent advances for removing heavy metals from water, soil and food, providing valuable guidance for environmental engineers and researchers seeking to address contamination challenges.

Selective adsorption of tetracycline and copper(II) on ion-imprinted porous alginate microspheres: performance and potential mechanisms

A novel epichlorohydrin and thiourea grafted porous alginate adsorbent (UA-Ca/IIP) was synthesized using ion-imprinting and direct templating to remove copper ions (Cu(II)) and tetracycline (TC) in aqueous solution. UA-Ca/IIP demonstrated great selectivity for Cu(II) and TC among different coexisting anions (CO32-, PO43- and SO42-), cations (Ca2+, Mg2+ and NH4+), and antibiotics (oxytetracycline and sulfamethoxazole). The adsorption of TC and Cu(II) by UA-Ca/IIP was significantly affected by the pH of the solution, and the quantity of TC and Cu(II) adsorbed reached a maximum at pH 5. A pseudo-second-order model better fitted the kinetic data; the Langmuir model predicted the maximum adsorption quantities 3.527 mmol TC g-1 and 4.478 mmol Cu(II) g-1 at 298 K. Thermodynamic studies indicated that the TC and Cu(II) adsorption was more rapid at a higher temperature. Antagonistic and synergistic adsorption experiments showed that the adsorption capacity of TC would increase significantly with the increase of Cu(II) concentration. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that along with the influence of pH, electrostatic interaction and complexation were the main mechanisms of TC and Cu(II) adsorption. Regeneration experiments revealed that TC and Cu(II) were removed efficiently and that UA-Ca/IIP was recyclable over the long term. These results show that the modified porous alginate microsphere is a green and recyclable adsorbent, which has good selectivity and high adsorption performance for the removal of TC and Cu(II).

Biodegradable and hemocompatible alginate/okra hydrogel films with promising stability and biological attributes

Currently, combinations of natural polymers and semi-synthetic biomolecules have gained attention for food-packaging, drug delivery, coatings, and biomedical applications. In this work, cross-linking property of two biopolymers was employed for the fabrication of hydrogel films. Sodium alginate (SAlg) and Okra gel (OkG) were used in different ratios (95:05, 75:25 and 85:15) to synthesize hydrogel films by solvent-casting method. Formation of the films was confirmed by FTIR and Raman techniques which specified the interaction between biomolecules of SAlg and OkG. XRD pattern has shown the presence of both amorphous and micro-crystalline phases in the hydrogel films and SEM studies have shown porosity, amorphousness and agglomerated morphology. TGA and DSC analyses revealed degradation of the film at 420 °C and stability studies using PBS buffer indicated stability and hydrophilic nature of hydrogel films. In-vitro degradation test was also performed for 10 weeks through the incubation of hydrogel-films in simulated body fluid and the effect of pH and temperature was also studied. Results have shown worth-some influence of okra gel on the fabricated films. Hemolytic and antioxidant activities of the gels were also determined and being non-toxic, all these ratios were found suitable for biomedical applications; especially 85:15 have shown maximum potential.

Adsorption of Copper and Arsenic from Water Using a Semi-Interpenetrating Polymer Network Based on Alginate and Chitosan

New biobased hydrogels were prepared via a semi-interpenetrating polymer network (semi-IPN) using polyacrylamide/chitosan (PAAM/chitosan) hydrogel for the adsorption of As(V) or poly acrylic acid/alginate (PAA/alginate) hydrogel for the adsorption of Cu(II). Both systems were crosslinked using N,N'-methylenebisacrylamide as the crosslinker and ammonium persulfate as the initiating agent. The hydrogels were characterized by SEM, Z-potential, and FTIR. Their performance was studied under different variables, such as the biopolymer effect, adsorbent dose, pH, contact time, and concentration of metal ions. The characterization of hydrogels revealed the morphology of the material, with and without biopolymers. In both cases, the added biopolymer provided porosity and cavities' formation, which improved the removal capacity. The Z-potential informed the surface charge of hydrogels, and the addition of biopolymers modified it, which explains the further metal removal ability. The FTIR spectra showed the functional groups of the hydrogels, confirming its chemical structure. In addition, the adsorption results showed that PAAM/chitosan can efficiently remove arsenic, reaching a capacity of 17.8 mg/g at pH 5.0, and it can also be regenerated by HNO₃ for six cycles. On the other hand, copper-ion absorption was studied on PAA/alginate, which can remove with an adsorption capacity of 63.59 mg/g at pH 4.0, and the results indicate that it can also be regenerated by HNO₃ for five cycles.

Preparation of sludge-cyanobacteria composite carbon for synergistically enhanced co-removal of Cu(II) and Cr(VI)

Traditional sludge disposal is currently restricted by the risk of secondary pollution. Sludge carbon material has gained widespread attention because of its low cost and environmentally sustainable properties. However, owing to the high ash content and low-energy density of sludge, sludge pyrolysis alone has certain limitations, and the performance of carbon materials needs to be improved. Herein, a sludge-cyanobacteria composite carbon (SCC) was easily synthesized, and the adsorption process of Cu(II) and Cr(VI) by SCC was examined. SCC-700-2-50% exhibited a high S_BET (1047.54 m²/g) and developed pore structure rich in functional groups (such as -NH, -OH, and C-O). The combination of pore structure and functional groups improved the adsorption performance of SCC. The adsorption processes exhibited a synergistic effect in a binary system: the q_m of Cu(II) and Cr(VI) were 386 mg/g and 341 mg/g, respectively, and the selectivity of Cu(II) adsorption by SCC was greater than Cr(VI). The adsorption process, examined by SEM-EDS, FTIR, and XPS analysis, indicated that Cu(II) as a cationic interface strengthens Cr(VI) adsorption through electrostatic interaction, and the anion Cr(VI) created a valid electrostatic shield against the electrostatic repulsion between H⁺ and Cu(II), facilitating Cu(II) adsorption. SCC had great reusability: Cu(II) and Cr(VI) adsorption capacity were 90% and 84%, of the initial adsorption capacity, respectively, after six cycles. This study demonstrates the prospect of SCC as a valid adsorbent for multiple heavy metal contaminations removal.

Research Progress of Polysaccharide-Based Natural Polymer Hydrogels in Water Purification

The pollution and scarcity of freshwater resources are global problems that have a significant influence on human life. It is very important to remove harmful substances in the water to realize the recycling of water resources. Hydrogels have recently attracted attention due to their special three-dimensional network structure, large surface area, and pores, which show great potential for the removal of pollutants in water. In their preparation, natural polymers are one of the preferred materials because of their wide availability, low cost, and easy thermal degradation. However, when it is directly used for adsorption, its performance is unsatisfactory, so it usually needs to be modified in the preparation process. This paper reviews the modification and adsorption properties of polysaccharide-based natural polymer hydrogels, such as cellulose, chitosan, starch, and sodium alginate, and discusses the effects of their types and structures on performance and recent technological advances.

Preparation of a novel hydrogel of sodium alginate using rural waste bone meal for efficient adsorption of heavy metals cadmium ion

Adsorption has been an important method for removing heavy metals from industrial wastewater. However, there has been a lack of an environmentally friendly, low-cost, biodegradable and easily recyclable material. China produces bones are not fully utilized leads to a waste of resources Therefore, efficient application of bone meal (BM) for remediation of contaminants in water would provide a promising alternative for resource utilization of bones. In this paper, we use a combination of BM and sodium alginate (SA) to prepare a novel BM/SA/calcium ion (BM/SA/Ca²⁺) double cross-linked composite hydrogel (BMSAH). Enhance the mechanical structure of SA while making the BM easy to recycle and reuse. The morphology and structure of the BMSAH were characterized using FT-IR spectroscopy and SEM-EDS. suggesting that the BMSAH can provide a larger specific surface area and high number of adsorption sites. The effects of the solution pH, ionic strength and contact time on the adsorption capacity of the BMSAH were investigated in depth, Under different conditions, BMSAH has a strong adsorption capacity of >90 %. XPS and FT-IR analysis showed that Cd²⁺ was adsorbed mainly via coordination interactions and hydrogen bonds with the carboxyl groups and nitrogen atoms in the BMSAH. A pseudo-second-order kinetic model, particle diffusion model and Isothermal adsorption lines indicate that the surface of the BMSAH is non-uniform suggesting that the adsorption of heavy metal ions by the BMSAH involves a combination of surface adsorption and intraparticle diffusion mechanisms, which is an overall chemical-physical adsorption process. In addition, the adsorption capacity of BMSAH remained above 90 % after three desorption cycles. Our work provides a new method for the preparation of a low-cost, high mechanical performance, biodegradable and easily recyclable physical hydrogels used for the removal of heavy metal ions.

Turning waste into valuables: In situ deposition of polypyrrole on the obsolete mask for Cr(VI) removal and desalination

The global mask consumption has been exacerbated because of the coronavirus disease 2019 (COVID-19) pandemic. Simultaneously, the traditional mask disposal methods (incineration and landfill) have caused serious environmental pollution and waste of resources. Herein, a simple and green mass-production method has been proposed to recycle carbon protective mask (CPM) into the carbon protective mask/polydopamine/polypyrrole (CPM/PDA/PPy) composite by in situ polymerization of PPy. The CPM/PDA/PPy composite was used for the removal of Cr(VI) and salt ions to produce clean water. The synergistic effect of PPy and the CPM improved the removal capability of Cr(VI). The CPM/PDA/PPy composite provided high adsorption capacity (358.68 mg g^-1) and economic value (811.42 mg $^-1). Consequently, the CPM/PDA/PPy (cathode) was combined with MnO₂ (anode) for desalination in CDI cells, demonstrated excellent desalination capacity (26.65 mg g^-1) and ultrafast salt adsorption rate (6.96 mg g^-1 min^-1), which was higher than conventional CDI cells. Our work proposes a new low-carbon strategy to recycle discarded masks and demonstrates their utilization in Cr(VI) removal and seawater desalination.

Enhanced treatment of landfill leachate by biochar-based aerobic denitrifying bacteria functional microbial materials: Preparation and performance

Objective

In this work, polyvinyl alcohol (PVA) and sodium alginate (SA) were used as entrapped carriers and Artemisia argyi stem biochar (ABC) was used as an absorption carrier to immobilize aerobic denitrifying bacteria screened from landfill leachate, thus a new carbon-based functional microbial material (PVA/SA/ABC@BS) was successfully prepared.

Methods

The structure and characteristics of the new material were revealed by using a scanning electron microscope and Fourier transform infrared spectroscopy, and the performance of the material for treating landfill leachate under different working conditions was studied.

Results

ABC had abundant pore structures and that the surface contained many oxygen-containing functional groups, carboxyl groups, and amide groups, etc. and it had good absorbing performance and strong acid and alkali buffering capacity, which was beneficial to the adhesion and proliferation of microorganisms. After adding ABC as a composite carrier, the damage rate of immobilized particles was decreased by 1.2%, and the acid stability, alkaline stability, and mass transfer performance were increased by 9.00, 7.00, and 56%, respectively. When the dosage of PVA/SA/ABC@BS was 0.017g/ml, the removal rates of nitrate nitrogen (NO₃ ^--N) and ammonia nitrogen (NH₄ ⁺-N) were the highest, which were 98.7 and 59.4%, respectively. When the pH values were 11, 7, 1, and 9, the removal rates of chemical oxygen demand (COD), NO₃ ^--N, nitrite nitrogen (NO₂ ^--N) and NH₄ ⁺-N reached the maximum values, which were 14.39, 98.38, 75.87, and 79.31%, respectively. After PVA/SA/ABC@BS was reused in 5 batches, the removal rates of NO₃ ^--N all reached 95.50%.

Conclusion

PVA, SA and ABC have excellent reusability for immobilization of microorganisms and degradation of nitrate nitrogen. This study can provide some guidance for the great application potential of immobilized gel spheres in the treatment of high concentration organic wastewater.

Fabrication of a waste cotton fabrics-based nanosystem for simultaneous removal of Cu(II) and Pb(II)

Herein, a waste cotton fabrics-based nanosystem was fabricated to simultaneously remove copper (Cu(II)) and lead ions (Pb(II)) from water and soil. Therein, carboxyl-functionalized zinc oxide microsphere (ZnO-COOH) with peanut shape was carried by cotton fabric (CF) to get CF/ZnO-COOH nanosystem. CF/ZnO-COOH with a good foldable property possessed a high removal capacity for Cu(II) and Pb(II) via electrostatic attraction and chelation. The result indicated that their removal efficiencies of CF/ZnO-COOH could reach over 95% after 2 h. The adsorption process was consistent with Langmuir (R² = 0.9905 of Cu(II) and R² = 0.9846 of Pb(II)) and pseudo-second-order kinetic models (R² = 0.9999 of Cu(II) and R² = 0.9999 of Pb(II)). The thermodynamic data showed that the adsorption process was spontaneous and exothermic. Additionally, CF/ZnO-COOH also possessed a high fixation ability for Cu(II) and Pb(II) in sand-soil column, especially for Pb(II) (15 cm, 0.4 μg kg^-1). Therefore, this wok provides an environmentally friendly and efficient way to remove Cu(II) and Pb(II) from water and soil concurrently.

In-house fabrication of macro-porous biopolymeric hydrogel and its deployment for adsorptive remediation of lead and cadmium from water matrices

A novel adsorbent was prepared by blending chitosan (CS) and acrylic acid (AA) while using formaldehyde as a cross linker in the form of hydrogel beads. The adsorption properties of these hydrogel beads for the removal of toxic metal ions (Pb²⁺ and Cd²⁺) from aqueous solutions were evaluated. The hydrogel beads have a 3D macro-porous structure whose -NH₂ groups were considered to be the dominant binding specie for Cd and Pb ions. The equilibrium adsorption capacity (q_e) of beads was significantly affected by the mass ratio of sorbent and sorbate. The percentage removal of Cd and Pb ions was observed to be enhanced with the increase in sorbate concentration. The hydrogel beads maintained good adsorption properties at adsorption-desorption equilibrium. The Langmuir and Freundlich models were used to elaborate the isotherms as well as isotherm constants. Adsorption isothermal data is well explained by the Freundlich model. The data of experimental kinetics is interrelated with the second-order kinetic model, which showed that the chemical sorption phenomenon is the rate limiting step. The results of intraparticle diffusion model described the adsorption process occurred on a porous substance that proved chitosan/Formaldehyde beads to be the favorable adsorbent.

Polymeric biomolecules based nanomaterials: Production strategies and pollutant mitigation as an emerging tool for environmental application

The ever-exploding global population coupled with its anthropogenic impact has imparted unparalleled detrimental effects on the environment and mitigating them has emerged as the prime challenge and focus of the current century. The niche of nanotechnology empowered by composites of biopolymers in the handling of xenobiotics and environmental clean-up has an unlimited scope. The appositeness of biopolymer-nanoparticles (Bp-NPs) for environmental contaminant mitigation has received unique consideration due to its exclusive combination of physicochemical characteristics and other attributes. The current review furnishes exhaustive scrutiny of the current accomplishments in the development of Bp-NPs and biopolymer nanomaterials (Bp-NMs) from various polymeric biomolecules. Special attention was provided for polymeric biomolecules such as cellulose, lignin, starch, chitin, and chitosan, whereas limited consideration on gelatin, alginate, and gum for the development of Bp-NPs and Bp-NMs; together with coverage of literature. Promising applications of tailored biopolymer hybrids such as Bp-NPs and Bp-NMs on environmentally hazardous xenobiotics handling and pollution management are discussed as to their notable environmental applications.

Evaluation of diethylenetriaminepentaacetic acid modified chitosan immobilized in amino-carbmated alginate matrix as a low cost adsorbent for effective Cu(II) recovery

In present work, facile synthesis of a biocompatible hybrid biosorbent based on diethylenetriaminepentaacetic acid (DTPA) modified chitosan immobilized in organo-functionalized sodium alginate matrix (DTPA-MCSA) was carried out. DTPA-MCSA was casted in microspherical hydrogel beads. Three dimensional microporous geometry of the biosorbent remained well preserved as observed in SEM analysis which revealed the improved mechanical strength of the alginate matrix. Surface functionalization of base biopolymers was confirmed by FTIR and SEM analysis. Equilibrium sorption studies using DTPA-MCSA for Cu(II) from aqueous medium were carried out in batch mode and found considerably dependent on pH, contact sorption time, temperature and initial copper concentration. Isothermal sorption data showed close correlation with Langmuir model as evident from nonlinear fitting of data (R 2 ˜ 0.99) at different temperatures. The experimental sorption capacity (q e) was found nearly 67 mg/g using 100 mg/L initial concentration of copper ions. Kinetic studies were conducted using different initial concentrations for better elucidation of results and it showed better correlation with pseudo second order rate equation which unveiled that strong ion pair coordination and complexation exist between Cu(II) and newly grafted chelating sites of DTPA-MCSA. Thermodynamic parameters suggested that the adsorption process is spontaneous and endothermic. The results concluded that DTPA-MCSA could be a better candidate for adsorptive remediation of copper ions from liquid waste.

Effective biosorption of Cu(II) using hybrid biocomposite based on N-maleated chitosan/calcium alginate/titania: Equilibrium sorption, kinetic and thermodynamic studies

In this research work, a hybrid biocomposite based on N-maleated chitosan, amino-thiocarbamate functionalised calcium alginate and anhydrous Titania nanoparticles (NMC-MCA-TiO₂) was fabricated. The study involves the one pot facile synthesis of N-maleated chitosan and amino-thiocarbamate functionalised alginate under moderate conditions. Sorbent was conditioned in the form of hydrogel beads and characterized through FT-IR and SEM analysis. Newly grafted functional groups could act as potential chelating sites for enhanced Cu(II) sorption. Modified biopolymers were organo-functionalised which provided excellent support for immobilization of Titania nanoparticles (TiO₂) as inorganic filler. Kinetic data illustrated the manifestation of intrinsic chemisorption instead of simple bulk/film diffusion. Equilibrium sorption data fitted well with Freundlich adsorption model (R² ≈ 0.99) which designated the heterogeneous nature of sorbent. Maximum sorption capacity of biosorbent was found 192 mg/g at 298 K and pH = 6.0. Standard Gibbs free energy change ∆G^o (-21.53, -21.97, and - 22.42 kJ/mol), standard enthalpy change ∆H^o (5.12 kJ/mol) and standard entropy change ∆S^o (0.09 kJ/mol K^-1) values suggested that the sorption process to be spontaneous and endothermic. The sorbent 3NMC-MCA-TiO₂ could be competitive candidate for economical and rapid adsorptive removal of Cu(II) from dilute contaminated liquids.

Upcycling of blending waste plastics as zwitterionic hydrogel for simultaneous removal of cationic and anionic heavy metals from aqueous system

Upcycling of waste plastics as functional materials is a new approach for synthesizing low-cost and durable adsorbents with zwitterionic property. Herein, a facile process for recycling blending waste plastics to fabricate zwitterionic plastic-g-hydrogel (ZPH) for simultaneous adsorbing cationic and anionic heavy metals was developed. ZPH possessed high affinities for cations and anions in both acid and alkaline conditions owing to its zwitterionic property, and the maximum adsorption capacities of Pb²⁺, Cd²⁺, Ba²⁺, and Cr(VI) (Cr₂O₇^2-) were 132.13, 85.58, 69.92 and 85.15 mg/g, respectively. Mechanism study indicated the incompatibility of blending plastics was skillfully overcome through the crosslinking between sodium alginate (SA)/chitosan (CTS) and plastics. Cations were adsorbed onto ZPH via electrostatic interaction, cation exchange and coordination interactions with Cl/N/O-containing groups. Furthermore, the reduction of Cr(VI) to Cr(III) was another important path for ZPH to capture anionic Cr₂O₇^2-, and subsequently Cr(III) was adsorbed via coordination interaction and cation exchange. Moreover, the regeneration experiment showed ZPH possessed excellent reusability and stable structure. Accordingly, this research provides a profitable approach for recycling blending plastics, and ZPH has potentials for industrial application in wastewater treatment or contaminated site remediation with complex heavy metals pollution.

Photocatalytic Removal of Cr(VI) by Thiourea Modified Sodium Alginate/Biochar Composite Gel

Heavy metal pollution is an important problem in current water treatments. Traditional methods for treating chromium-containing wastewater have limitations such as having complicated processes and causing secondary pollution. Therefore, seeking efficient and fast processing methods is an important research topic at present. Photocatalysis is an efficient method to remove Cr(VI) from aqueous solutions; however, conventional photocatalysts suffer from a low metal absorption capacity, high investment cost, and slow desorption of trivalent chromium from the catalyst surface. In this study, a novel composite gel was synthesized by chemically modifying thiourea onto sodium alginate, which was then mixed with biochar. The composite gel (T-BSA) can effectively remove 99.98% of Cr(VI) in aqueous solution through synergistic adsorption and photocatalytic reduction under UV light irradiation. The removal mechanism of Cr(VI) was analyzed by FT-IR, FESEM, UV-DRS and XPS. The results show that under acidic conditions, the amino group introduced by chemical modification can be protonated to adsorb Cr(VI) through electrostatic interaction. In addition, the biochar as a functional material has a large specific surface area and pore structure, which can provide active sites for the adsorption of Cr(VI), while the photo-reduced Cr(III) is released into the solution through electrostatic repulsion, regenerating the adsorption sites, thereby improving the removal performance of Cr(VI). Biochar significantly intensifies the Cr(VI) removal performance by providing a porous structure and transferring electrons during photoreduction. This study demonstrates that polysaccharide-derived materials can serve as efficient photocatalysts for wastewater treatment.

Heavy metal-contained wastewater in China: Discharge, management and treatment

A large amount of heavy metal-contained wastewater (HMW) was discharged during Chinese industry development, which has caused many environmental problems. This study reviewed discharge, management and treatment of HMW in China through collecting and analyzing data from China's official statistical yearbook, standards, technical specifications, government reports, case reports, and research paper. Results showed that industry wastewater discharged by an amount of about 221.6 × 10⁸ t (in 2012), where emission of heavy metals including Pb, Hg, Cd, Cr(VI), T-Cr was around 388.4 t (in 2012). Heavy metal emission with wastewater in east China and central south China was observed to be graver than that in other areas. However, control of heavy metals in Pb and Cd in northwest China was more difficult compared with other areas. In terms of management, China's government has issued many wastewater discharge standards, strict management policies for controlling HMW discharge in recent years, resulting in reduced HMW discharge. In addition, main HMW treatment technology in China was chemical precipitation, and other technologies such as membrane separation, adsorption, ion exchange, electrochemical and biological methods were also occasionally applied. In the future, chemical industries will be concentrated in northwest China, therefore control of HMW discharge should be paid much more attention in those areas. In addition, more effective and environment-friendly heavy metal removal and regeneration technologies should be developed, such as biomaterials adsorbent.

The aggregation behaviour and mechanism of commercial graphene oxide in surface aquatic environments

In this study, we comprehensively and critically discuss the aggregation mechanism of commercial graphene oxide (CGO) in surface aquatic environments. The aggregation kinetics and critical coagulation concentration of CGO were obtained through time-resolved dynamic light scattering and batch techniques over a wide range of water types. By employing transmission electron microscopy and elemental mapping, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, we studied the effects of cations in natural waters on the microstructure transformation, element content and distribution, and oxygen-containing functional group vibrations of CGO. The aggregation of CGO in natural water is induced mainly by Ca²⁺ by complexing; Na⁺, with a higher concentration, plays a more important role than Mg²⁺ in inducing aggregation via electric double layer suppression. Ca²⁺ mainly interacts with C - COOH, while Mg²⁺ has a greater effect on C - OH. Na⁺ has less effect on the oxygen-containing functional group but decreases the C/O ratio in contrast with Mg²⁺/Ca²⁺/natural water, indicating the different inducing mechanisms. This study looks forward to providing pivotal knowledge to predict the environmental fate of CGO more accurately in natural surface water.

Enhanced selective adsorption of lead(II) from complex wastewater by DTPA functionalized chitosan-coated magnetic silica nanoparticles based on anion-synergism

Simultaneously removing heavy metal and dye from complex wastewater is of great significance to industrial wastewater treatment. Herein, a novel magnetic adsorbent, DTPA-modified chitosan-coated magnetic silica nanoparticle (FFO@Sil@Chi-DTPA), was successfully prepared and used to enhance the Pb(II) selective adsorption from multi-metal wastewater based on anion-synergism. In the competitive experiment conducted in a multi-ion solution, the type of selective adsorption of metals was changed by the adsorbents before and after amidation, in which FFO@Sil@Chi-DTPA exhibited an excellent selectively for capturing Pb(II), while FFO@Sil@Chi demonstrated highly selective adsorption of silver. More importantly, the selective adsorption of Pb(II)S by FFO@Sil@Chi-DTPA was enhanced from 111.71 to 268.01 mg g^-1 when the coexisting MB concentrations ranged from 0 to 100 mg L^-1 at pH 6.0. In the Pb(II)-MB binary system, Pb(II) and MB exhibited a synergistic effect, in which the presence of MB strengthened the adsorption effect of Pb(II) due to the sulfonic acid groups in MB molecules that create new specific sites for Pb(II) adsorption, while MB adsorption was also enhanced by the presence of Pb(II). This work provides a new strategy for exploring novel adsorbents that can enhance the selective removal of heavy metal in complex wastewater based on anion-synergism.

Development of Pectin-Based Aerogels with Several Excellent Properties for the Adsorption of Pb2

Traditional aerogels lack specific functional groups for the adsorption of Pb2+, which results in a low adsorption capacity and limits the application scope. Novel porous pectin-based aerogels (PPEAs) were prepared by incorporating polyethylenimine (PEI) using ethylene glycol diglycidyl ether (EGDE) as a cross-linker for the removal of Pb2+ from water. The cross-linking mechanism, morphology, mechanical strength, thermal stability, adsorption properties, and mechanism of the aerogels were investigated. The aerogels possessed several desirable features, such as a large maximum Pb2+ adsorption capacity (373.7 mg/g, tested at pH 5.0), ultralight (as low as 63.4 mg/cm3), high mechanical strength (stress above 0.24 MPa at 50% strain), and easy recyclability. Meanwhile, the equilibrium adsorption data was well described by the Langmuir-Freundlich (Sips) model and the kinetic adsorption process was well fitted using the pseudo-second-order model. The donor groups, such as -NH2, and oxygen-containing functional groups were responsible for the Pb2+ adsorption, which was confirmed by the FTIR and XPS analysis. The excellent characteristics mean that PPEAs are highly effective adsorbents in the remediation of lead-containing wastewater.