Polyethylenimine-functionalized silk sericin beads for high-performance remediation of hexavalent chromium from aqueous solution

Continuous treatment of highly concentrated tannery wastewater using novel porous composite beads: Central composite design optimization study

This present study depicts the successful employment of fixed-bed column for total chromium removal from tannery wastewater in dynamic mode using sodium alginate-powdered marble beads (SA-Marble) as adsorbent. The SA-Marble composite beads prepared were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Brunauer, Emmett and Teller (BET) method. The adsorption process performance of this bio-sorbent was examined in batches and columns for real effluent (tannery wastewater). After 90 min, the total chromium removal efficiency could be kept above 90% in the batch experiment. The adsorption kinetics fit better with the pseudo-second-order model, indicating the chemisorption process and the adsorption capacity of about 67.74 mg g-1 at 293 K (C0 = 7100 mg L-1) was obtained. Additionally, dynamic experiments indicate that the total chromium removal efficiency could be maintained above 90% after 120 min at 293 K and 60 min at 318 and 333 K; it's an endothermic but rapid process. The effects of two adsorption variables (Temperature and time) were investigated using central composite design (CCD), which is a subset of response surface methodology (total Cr, COD, sulfate, and total phosphorus percentage removal). This work paves a new avenue for synthesizing SA-Marble composite beads and provides an adsorption efficiency of total chromium removal from tannery wastewater.

Graphical abstract

Effect of Sericin Content on the Structural Characteristics and Properties of New Silk Nonwoven Fabrics

Recently, natural silk nonwoven fabrics have attracted attention in biomedical and cosmetic applications because of their excellent biocompatibility, mechanical properties, and easy preparation. Herein, silk nonwoven fabrics were prepared by carding silk filaments to improve their productivity, and the effect of sericin content on the structure and properties of silk nonwoven fabrics was investigated. Owing to the binding effect of sericin in silk, a natural silk nonwoven fabric was successfully prepared through carding, wetting, and hot press treatments. Sericin content affected the structural characteristics and properties of the silk nonwoven fabrics. As the sericin content increased, the silk nonwoven fabrics became more compact with reduced porosity and thickness. Further, with increasing sericin content, the crystallinity and elongation of the silk nonwoven fabrics decreased while the moisture regain and the maximum stress increased. The thermal stability of most silk nonwoven fabrics was not affected by the sericin content. However, silk nonwoven fabrics without sericin had a lower thermal decomposition temperature than other nonwoven fabrics. Regardless of the sericin content, all silk nonwoven fabrics exhibited optimal cell viability and are promising candidates for cosmetic and biomedical applications.

Novel efficient capture of hexavalent chromium by polyethyleneimine/amyloid fibrils/polyvinyl alcohol aerogel beads: Functional design, applicability, and mechanisms

The harmful effects of hexavalent chromium (Cr(VI)) on the environment and human health have aroused wide public concern. In this study, bulk spherical aerogel beads (PAP) were synthesized from polyethyleneimine (PEI), protein amyloid fibrils (AFL), and polyvinyl alcohol (PVA) through green technology and its removal of Cr(VI) from wastewater was comprehensively studied. The results showed that although the bulk PAP beads (∼ 5 mm) only had an average pore size of 16.88 nm and a BET surface area of 12 m²/g, its maximum adsorption capacity for Cr(VI) reached 121.44 mg/g (at 298 K). Cr(VI) adsorption onto PAP conformed to pseudo-second-order adsorption kinetics and was endothermic. The adsorption of Cr(VI) decreased stepwise with the increase of solution alkalinity (pH = 2: 91.97%; pH = 10: 0.04%). Importantly, PAP showed high selectivity towards Cr(VI) in mixed heavy metal solutions (Cr(VI) > Pb(II) > Ni(II) > Cu(II) > Cd(II)) and good reusability (removal efficiency > 88% after 5 cycles). PAP had excellent anti-interference ability against FA and HCO₃^- with the overall removal rate exceeding 87% in the presence of 5 - 25 mg/L of these ions. Cations such as Na⁺, Mg²⁺, and other heavy metal ions at high concentrations could promote the removal efficiency of Cr(VI). The removal rates of Cr(VI) and Cr(III) by PAP in a tannery wastewater were 34.4% and 59.3%, respectively. Meanwhile, the removal rates of Cr(VI) in a electroplating wastewater and a contaminated soil leachate reached 84.4∼89.7%, showing high practicability. Mechanism studies revealed that electrostatic attraction, hydrogen bonding, reduction, and complexation were the main reactions for Cr(VI) removal by PAP. In general, the study of PAP provides a new insight into using bulk monolith materials for treating Cr(VI) contaminated wastewater.

Biomimetic Polylactic Acid Electrospun Fibers Grafted with Polyethyleneimine for Highly Efficient Methyl Orange and Cr(VI) Removal

The rapid growth of industrialization has resulted in the release of large quantities of pollutants into the environment, especially dyes and heavy metals, which are environmentally hazardous for humans and animals. It is considered as the most promising and environmentally friendly route to develop green materials by using the green modification method, which has no negative impact on the environment. In this work, the green material of polylactic acid (PLA) was used as the substrate material, and a novel modification method of polydopamine (PDA)-assisted polyethyleneimine (PEI) grafting was developed. The electrospun PLA fibers are mainly composed of stereocomplex crystallites, which were achieved via the electrospinning of poly(l-lactic acid) and poly(d-lactic acid). The water-soluble PEI was grafted onto the PDA-modified PLA fibers through the glutaraldehyde-assisted cross-linking reaction. The prepared composite fibers can be degraded, which is environmentally friendly and meets the requirements of sustainable development. The potential application of such PLA composite fibers in wastewater treatment was intensively evaluated. The results show that at appropriate fabrication conditions (PDA concentration of 3 g·L^-1 and a PEI molecular weight of 70,000 g·mol^-1), the composite fibers exhibit the maximum adsorption capacities of 612 and 398.41 mg·g^-1 for methyl orange (MO) and hexavalent chromium [Cr(VI)], respectively. Simultaneously, about 64.79% of Cr(VI) adsorbed on the composite fibers was reduced to Cr(III). The above results show that the PLA composite fibers have a good development prospect in the field of wastewater treatment.

Structural Characteristics and Properties of Cocoon and Regenerated Silk Fibroin from Different Silkworm Strains

Silk has attracted the attention of researchers as a biomedical and cosmetic material because of its good biocompatibility and cytocompatibility. Silk is produced from the cocoons of silkworms, which have various strains. In this study, silkworm cocoons and silk fibroins (SFs) were obtained from ten silkworm strains, and their structural characteristics and properties were examined. The morphological structure of the cocoons depended on the silkworm strains. The degumming ratio of silk ranged from 22.8% to 28% depending on the silkworm strains. The highest and lowest solution viscosities of SF were shown by 9671 and 9153, respectively, showing a 12-fold difference. The silkworm strains of 9671, KJ5, and I-NOVI showed a two-fold higher work of ruptures for the regenerated SF film than 181 and 2203, indicating that the silkworm strains considerably influence the mechanical properties of the regenerated SF film. Regardless of the silkworm strain, all silkworm cocoons showed good cell viability, making them suitable candidates for advanced functional biomaterials.

Silk sericin as building blocks of bioactive materials for advanced therapeutics

Silk sericin is a class of protein biopolymers produced by silkworms. Increasing attention has been paid to silk sericin for biomedical applications in the last decade, not only because of its excellent biocompatibility and biodegradability but also due to the pharmacological activities stemming from its unique amino acid compositions. In this review, the biological properties of silk sericin, including curing specific diseases and promoting tissue regeneration, as well as underlying mechanisms are summarized. We consider the antioxidant activity of silk sericin as a fundamental property, which could account for partial biological activities, despite the exact mechanisms of silk sericin's effect remaining unknown. Based on the reactive groups on silk sericin, approaches of bottom-up fabrication of silk sericin-based biomaterials are highlighted, including non-covalent interactions and chemical reactions (reduction, crosslinking, bioconjugation, and polymerization). We then briefly present the cutting-edge advances of silk sericin-based biomaterials applied in tissue engineering and drug delivery. The challenges of silk sericin-based biomaterials are proposed. With more bioactivities and underlying mechanisms of silk sericin uncovered, it is going to boost the therapeutic potential of silk sericin-based biomaterials.

Recent advancements in engineered biopolymeric-nanohybrids: A greener approach for adsorptive-remediation of noxious metals from aqueous matrices

Industrial wastewater is causing serious health problems due to presence of large concentrations of toxic metals. Removal of these metals is still a big challenge using pristine natural biopolymers due to their low surface area, water solubility, and poor recovery. Developing biopolymeric composites with other materials has attained attention because they possess a high surface area and structural porosity, high reactivity, and less water solubility. In simple words, biopolymeric nanohybrids have great adsorption capacity for heavy metals. Biopolymeric materials are abundant, low cost, biodegradable, and possess different functional moieties (carboxyl, amine, hydroxyl, and carbonyl) which play a vital role to adsorb metal ions through various inter-linkages (i.e., electrostatic, hydrogen bonding, ion exchange, chelation, etc.). Biopolymeric nanohybrids have been proven a potent tool in environmental remediation such as the abatement of heavy metal ions from polluted water. Herein, we have reported the adsorption potential of various biopolymers (cellulose, chitosan, pectin, gelatin, and silk proteins) for the removal of heavy metals. This review discusses the suitability of biopolymeric nanohybrids as an adsorbent for heavy metals, their synthesis, modification, adsorption potential, and adsorption mechanism along with best fitted thermodynamic and kinetic models. The influence of pH, contact time, and adsorbent dose on adsorption potential has also been discussed in detail. Lastly, the challenges, research gaps and recommendations have been presented. This review concludes that biopolymers in combination with other materials such as metal-based nanoparticles, clay, and carbon-based materials are excellent materials to remove metallic ions from wastewater. Significant adsorption of heavy metals was obtained at a moderate pH (5-6). Contact time and adsorbent dose also affect the adsorption of heavy metals in certain ways. The Pseudo-first order model fits the data for the initial period of the first step of the reaction. Kinetic studies of different adsorption processes of various biopolymeric nanohybrids described that for majority of bionanohybrids, Pseudo-second order fitted the experimental data very well. Functionalized biopolymeric nanohybrids being biodegradable, environment friendly, cost-effective materials have great potential to adsorb heavy metal ions. These may be the future materials for environmental remediation.

Strengthening the surface and adsorption properties of diatomite for removal of Cr(VI) and methylene blue dye

The main purpose of this work was to boost the surface and adsorption characteristics of diatomite (D) through chemical modifications with chitosan (DC), chitosan/titanium isopropoxide (DCTi), or chitosan/ graphene oxide (DCGr), respectively. Physicochemical characteristics of the prepared samples were investigated using SEM, TEM, XRD, FTIR, TGA, and porosity measurements. The impact of such modifiers into the D surface on the removal efficiency of chromium (VI) ions and methylene blue dye was studied in an equilibrium mode. Langmuir and Freundlich isotherms were used to analyze the adsorption data. Modifiers considerably enhanced the surface and textural properties of D through insertion of the main surface functional groups of chitosan and graphene oxide together compared to chitosan and titanium isopropoxide together or chitosan alone. In addition, the total surface area and total pore volume parameters of the unmodified D sample were improved greatly from 16.5 m2/g, 0.036 cm3/g to 39.8 m2/g and 0.174 cm3/g for DCGr, while they were 17.7 m2/g and 0.132 cm3/g for DC. The best adsorption results were well-defined with the Langmuir isotherm equilibrium model. Accordingly, the DCGr sample exhibited the highest uptake of Cr(VI) (about 167 mg/g) and methylene blue (66.7 mg/g). Hence, the chemical modification strategy of diatomite performed by using chitosan and graphene oxide significantly boosted the surface active sites and porosity properties and thus gave rise to the high adsorption capacity of Cr(VI) and methylene blue dye from wastewater. Hence, these findings affirmed the validity of the current strategy for surface modification of diatomite with chitosan and graphene oxide.

Theranostic silk sericin/SPION nanoparticles for targeted delivery of ROR1 siRNA: Synthesis, characterization, diagnosis and anticancer effect on triple-negative breast cancer

Triple-negative breast cancer (TNBC) has the worst prognosis among all breast cancer subtypes. The lack of proper treatments prompted scientists to find a practical targeted therapy to treat this type of tumor. Based on previous studies, tyrosine kinase-like orphan receptor (ROR1) is overexpressed in TNBC cells. Here, we designed a system consisting of superparamagnetic iron oxide nanoparticles (SPIONs) decorated with silk sericin (SS NPs) for the targeted delivery of ROR1 siRNA, a gene silencer to knockdown the expression of human ROR1 gene. NPs exhibited spherical shape of about 193 nm with acceptable properties both in vitro and in vivo. The apoptosis study showed significant death of MDA-MB-231 cells after 24 h treatment with the prepared NPs. The real-time PCR study also demonstrated an almost complete shutdown of ROR1 expression. Guided by magnetic field, enhanced accumulation of NPs was observed in breast tumors induced by 4T1 cells in BALB/c mice. Histological evaluation of the tumor exhibited necrosis 14 days post-treatment with the siRNA-loaded NPs; whereas, the untreated tumor was proliferating. Also, the tumor growth rate was significantly decreased after treatment with siRNA-loaded NPs in vivo. In conclusion, the prepared delivery system could be considered as a potential therapeutic strategy for treating TNBC.

Cationic surface-modified regenerated nanocellulose hydrogel for efficient Cr(VI) remediation

Because nanocellulose has a large specific surface area and abundant hydroxyl functional groups due to its unique nanomorphology, interest increases as an eco-friendly water treatment material. However, the distinctive properties of nanocellulose, which exists in a dispersion state, strongly hamper its usage in practical water treatment processes. Additionally, nanocellulose shows low performance in removing anionic pollutants because of its anionic characteristics. In an effort to address this challenge, regenerated cellulose (RC) hydrogel was fabricated through cellulose's dissolution and regeneration process using an eco-friendly aqueous solvent system. Subsequently, a crosslinking process was carried out to introduce the cationic functional groups to the RC surface PEI coating (P/RC). As a result, the PEI surface cationization process improved the mechanical rigidity of RC and showed an excellent Cr(VI) removal capacity of 578 mg/g. In addition, the prepared P/RC maintained more than 90% removal efficiency even after seven reuses.

Progress in surface-modified silicas for Cr(VI) adsorption: A review

Various toxic chemicals are discharging to the environment due to rapid industrialization and polluting soil, water, and air causing numerous diseases including life-threatening cancer. Among these pollutants, Cr(VI) or hexavalent chromium is one of the most carcinogenic and toxic contaminants hostile to human health and other living things. Therefore, along with other contaminants, the removal of Cr(VI) efficiently is very crucial to keep our environment neat and clean. On the other hand, silica has a lot of room to modify its surfaces as it is available with various sizes, shapes, pore sizes, surface areas etc. and the surface silanol groups are susceptible to design and prepare adsorbents for Cr(VI). This review emphases on the progress in the development of different types of silica-based adsorbents by modifying the surfaces of silica and their application for the removal of Cr(VI) from wastewater. Toxicity of Cr(VI), different silica surface modification processes, and removal techniques are also highlighted. The adsorption capacities of the surface-modified silica materials with other parameters are discussed extensively to understand how to select the best condition, silica and modifiers to achieve optimum removal performance. The adsorption mechanisms of various adsorbents are also discussed. Finally, future prospects are summarized and some suggestions are given to enhance the adsorption capacities of the surface-modified silica materials.

Polydopamine-assisted polyethylenimine grafting melamine foam and the application in wastewater purification

Melamine foam (MF) is a widely used commercial product and exhibits wide applications in many fields ranging from building, transportation to daily chemical product. Recent researches confirm that the special three-dimensional (3D) framework structure of MF can be an ideal substrate to prepare functional materials. In this work, the water-soluble polyethylenimine (PEI) was grafted onto the framework of MF to develop the water purification material toward heavy metal ions removal. The grafting of PEI on MF was achieved with the aids of polydopamine (PDA) coating and epoxy chloropropane (ECH) cross-linking successively. The 3D framework of MF could be well reserved and PEI was homogeneously grafted onto the framework surface. The adsorption capacity of the adsorbent was dependent upon the molecular wight of PEI. Lower PEI molecular weight endowed the adsorbent with better adsorption ability. The maximum adsorption capacity reached 328.95 mg/g, and the adsorbent exhibited extremely high adsorption stability with increasing cycling measurement numbers. Further results showed that the adsorbent also exhibited high reduction ability and induced about 62.5% toxic Cr(VI) to be reduced. This work confirms that the PEI-modified MF sample is a promising adsorbent in the removal of heavy metal ions and it can be used in wastewater treatment.

Effect of chlorhexidine gluconate on mechanical and anti-microbial properties of thermoplastic cassava starch

Antimicrobial thermoplastic starch (TPS) was developed using cassava starch, glycerol, and chlorhexidine gluconate (CHG) blend. CHG was added at concentrations of 1%, 5%, 10%, and 20% (wt./wt.) as an antimicrobial additive. The tensile strength and hardness of the blended samples increased with the chlorhexidine gluconate content, especially for 1% CHG. wt./wt. (12.6 MPa and 94, respectively). The TPS/CHG20 blend exhibited a large phase of CHG and recrystallization of TPS. The water solubility decreased with the addition of CHG. Nuclear magnetic resonance data confirmed a reaction between the hydroxyl groups of TPS and the amino groups of CHG. The TPS/CHG20% exhibited an inhibition zone for three bacterial types (Staphylococcus aureus, Escherichia coli, and Bacillus cereus) and three fungal types (Rhizopus oligosporus, Aspergillus oryzae, and Candida albicans). CHG acted simultaneously as a chain extender and an antimicrobial additive for TPS, improving its tensile strength, hardness, and anti-microbial properties.

Sericin cocoon bio-compatibilizer for reactive blending of thermoplastic cassava starch

Cassava starch was blended with glycerol to prepare thermoplastic starch (TPS). Thermoplastic starch was premixed with sericin (TPSS) by solution mixing and then melt-blended with polyethylene grafted maleic anhydride (PEMAH). The effect of sericin on the mechanical properties, morphology, thermal properties, rheology, and reaction mechanism was investigated. The tensile strength and elongation at break of the TPSS10/PEMAH blend were improved to 12.2 MPa and 100.4%, respectively. The TPS/PEMAH morphology presented polyethylene grafted maleic anhydride particles (2 μm) dispersed in the thermoplastic starch matrix, which decreased in size to approximately 200 nm when 5% sericin was used. The melting temperature of polyethylene grafted maleic anhydride (121 °C) decreased to 111 °C because of the small crystal size of the polyethylene grafted maleic anhydride phase. The viscosity of TPS/PEMAH increased with increasing sericin content because of the chain extension. Fourier-transform infrared spectroscopy confirmed the reaction between the amino groups of sericin and the maleic anhydride groups of polyethylene grafted maleic anhydride. This reaction reduced the interfacial tension between thermoplastic starch and polyethylene grafted maleic anhydride, which improved the compatibility, mechanical properties, and morphology of the blend.

Thermoplastic mung bean starch/natural rubber/sericin blends for improved oil resistance

Oil resistant thermoplastic elastomers (TPE) were prepared using mung bean thermoplastic starch (MTPS) blending with rubbers and sericin. Sericin was incorporated into MTPS as a compatibilizer. MTPS with sericin (MTPSS) was blended with natural rubber (NR) and epoxidized NR (ENR). Sericin at 5% improved the tensile strength (10 MPa), elastic recovery (52%) and morphology of the MTPSS/ENR blend. The mechanical properties, elastic recovery and morphology of the MTPSS5/NR blend were improved by the addition of ENR. The MTPSS/ENR showed palm (28%) and motor oils (8%) swelling resistance because of the hydrophilicity of MTPS and high polarity of ENR. The MTPSS/ENR/NR showed gasoline swelling resistance (104%) because of the hydrophilicity of MTPS and low polarity of NR. FTIR confirmed a reaction between the -NH groups of sericin and the epoxy groups of ENR. This reaction improved the compatibility, mechanical properties, elastic recovery, morphology and oils swelling resistance of the blends.

Underwater suspended bifunctionalized polyethyleneimine-based sponge for selective removal of anionic pollutants from aqueous solution

Highly selective and efficient removal of ionic pollutants, including ionic organic compounds and heavy metal ions from water, is still a huge challenge due to the complex nature of polluted water. To meet this challenge, we presented the synthesis of bifunctionalized polyethyleneimine-based sponges through cryo-polymerization via BDDE as the crosslinker followed by bifunctional modification with glycidyl trimethylammonium chloride (GTAC) and phenyl glycidyl ether (PGE), which simultaneously afford quaternary ammonium cation (strongly basic and hydrophilic) and phenyl (hydrophobic) functionalities, respectively. As a result, a hybrid hydrophilic-hydrophobic sponge is generated that could stably be suspended underwater due to the co-operative effect of the water-absorbing hydrophilic domain and the hydrophobic domain generating buoyancy. The quaternized and phenyl-functionalized PEI-based sponge (S_QP-PEI) demonstrated highly selective and efficient removal of anionic pollutants from water, including diclofenac sodium (DIC), methyl orange (MO) and chromium (Cr(VI)) with co-existing interferences. The Langmuir isotherms revealed the maximum adsorption capacities of 342.7 mg/g, 491.9 mg/g, and 242.7 mg/g for DIC, MO, and Cr(VI), respectively. The studies of adsorption mechanism suggested that the bifunctional S_QP-PEI sponge indeed afford both strong anion-exchange interaction and π-π interaction toward organic pollutants DIC and MO, and the strong anion-exchange interaction can be the dominated adsorption mechanism for anionic DIC, MO and Cr(VI) species. The suspended S_QP-PEI also demonstrated excellent reusability, which shows the potential of S_QP-PEI for real applications.

Engineering silk sericin decorated zeolitic imidazolate framework-8 nanoplatform to enhance chemotherapy

The low therapeutic effect and strong side-effect are the major barriers for clinical chemotherapy. Herein, a pH-responsive nanoplatform based-silk sericin-zeolitic imidazolate framework-8 was designed for the delivery of chemotherapeutic doxorubicin (denoted as ZIF-8@DOX@SS, ZDS), which can overcome the limitation of poor circulation stability and unexpected drug leakage in blood circulation, producing a satisfactory chemotherapy. Concretely, ZIF-8 structure shows better stability and biocompatibility owing to the protection of a nature and non-toxic sericin protein. When it comes to low pH environment (e.g. in tumor cell microenvironment), the coordination effect in ZIF-8 will be broken and release DOX drugs. The nano-sized morphology endow ZDS an efficient drug uptake and significant tumor permeability efficiency. Furthermore, the tumor-specific biodegradability makes ZDS possible to realize targeted and enhanced chemotherapy. Considering all the advantages in the study, this silk sericin-based nanosystem represent a promising strategy for the design of stimuli-responsive by using natural polymer to improve the treatment effect of chemotherapy.

Fast removal of heavy metals from water and soil samples using magnetic Fe3O4 nanoparticles

Heavy metal discharge from anthropogenic sources on open soil surfaces and in natural water bodies poses serious environmental and health concerns. In addition to the contamination reduction of metals at the source, post-discharge removal of metals using nanoparticles is one of the remediation technologies being explored nowadays due to its cost-effectiveness, being environment-friendly, and easy application as a technique. In this work, magnetic iron oxide (Fe₃O₄) nanoparticles were synthesized chemically and then used for the removal of heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, and Zn) from water and soil samples. The heavy metal removal efficiency of these iron oxide nanoparticles for different metals in water was best observed at a pH of 4.5 and varied between 63.5 and 98.3%. However, the removal efficiency of these nanoparticles from the soil sample was only measured at a pH of 0.7, and heavy metal removal efficiency varied between 69.6 and 99.6%. In both soil and water samples, the most efficient remediation time was less than 20 min, after which desorption and even dissolution of the nanoparticles can occur at a highly acidic pH. Among all selected metals for removal, lead showed the best adsorption and hence removal efficiency. The nanoparticles were characterized using the TEM, XRD, and FTIR techniques. The adsorption efficiency of various metals was estimated by using atomic absorption spectroscopy. The results suggest that the removal efficiency and stability of adsorbed products can further be improved by adjusting the pH higher towards 7 and also perhaps by modifying the nanoparticles with functional groups. The primary advantage of the magnetic un-coated nanoparticles is easy and efficient removal of the nanoparticles from the treated solutions by using an ordinary magnet.

Facile synthesis of Zr4+ incorporated chitosan/gelatin composite for the sequestration of Chromium(VI) and fluoride from water

The development of industrialization and agricultural activities have carried various negative impacts to living organisms in recent decades and also, the frequent problem of inorganic pollution have been environmental anxiety to the community. Among these, Cr⁶⁺ and F^- are priority poisonous pollutants from many industries. In this work, we present a low-cost synthesis procedure to obtain biocompatible zirconium incorporated chitosan-gelatin composite (CS-Zr-GEL) were fabricated and explored for the adsorptive removal of toxic Cr⁶⁺ and F^- from water. The adsorption mechanism of toxic Cr⁶⁺ and F^- was done by batch mode as a function of contact time, solution pH and co-existing ions. The obtained materials were extensively studied by several physico-chemical techniques to access their properties by X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analysis. Additionally, the fabricated adsorbent is highly dependent on solution pH. The kinetic and isotherm data were fitted using pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity for CS-Zr-GEL is 138.89 and 12.13 mg/g at 323K for Cr⁶⁺ and F^- respectively. These findings demonstrate that the CS-Zr-GEL adsorbent represents a promising candidate that would have a practical influence on water/wastewater treatments.

Micro-Plasma Assisted Synthesis of ZnO Nanosheets for the Efficient Removal of Cr6+ from the Aqueous Solution

Herein, we report a micro-plasma assisted solvothermal synthesis and characterization of zinc oxide nanosheets (ZnO-NSs) and their application for the removal of Cr6+ ion from aqueous solution. The morphological investigations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the high-density growth of nanosheets with the typical sizes in the range of 145.8–320.25 nm. The typical surface area of the synthesized ZnO-NSs, observed by Brunauer-Emmett-Teller (BET), was found to be 948 m2/g. The synthesized ZnO-NSs were used as efficient absorbent for the removal of Cr6+ ion from aqueous solution. Various parameters such as pH, contact time, amount of adsorbate and adsorbent on the removal efficiency of Cr6+ ion was optimized and presented in this paper. At optimized conditions, the highest value for removal was 87.1% at pH = 2 while the calculated maximum adsorption capacity was ~87.37 mg/g. The adsorption isotherm data were found to be best fitted to Temkin adsorption isotherm and the adsorption process followed the pseudo-first-order kinetics. Furthermore, the toxicity of ZnO-NSs were also examined against fibroblast cells, which show favorable results and proved that it can be used for wastewater treatment.

The magnetic covalent organic framework as a platform for high-performance extraction of Cr(VI) and bisphenol a from aqueous solution

The magnetic covalent organic framework with β-ketoenamine linkage (Fe₃O₄@COF(TpPa-1)) was fabricated by the hydrothermal method. The obtained Fe₃O₄@TpPa-1 integrated four advantages, namely easy preparation, high stability, excellent adsorption performance (485.2 m²/g) and good recoverability (19.5 emu/g), which enabled it an ideal sorbent for wastewater treatment. Fe₃O₄@TpPa-1 exhibited excellent adsorption capacities for Cr (VI) (245.45 mg/g) and bisphenol A (1220.97 mg/g). The adsorption kinetics and isotherms were in alignment to the pseudo-second-order and Langmuir model, respectively. After five times cycles, the adsorption capacity of Fe₃O₄@TpPa-1 still retained at a high level. According to Materials Studio simulation and XPS analysis, the adsorption mechanism was attributed to the presence of the homogeneously distributed imine and carbonyl functional groups in the framework of TpPa-1, allowing them to serve as platforms for anchoring heavy metals and organic pollutants. Besides, the hydrophobic skeleton structures of TpPa-1 endowed them good adsorption performance towards organic pollutants via hydrogen -bonding (NH^…O^…HO) and π-π interaction. Therefore, the recyclable Fe₃O₄@TpPa-1 showed a broad application prospects in environmental remediation.

Biosorption of hexavalent chromium from aqueous solution by polyethyleneimine-modified ultrasonic-assisted acid hydrochar from Sargassum horneri

In this study, an efficient route to synthesizing polyethyleneimine-modified ultrasonic-assisted acid hydrochar (PEI-USAH) is developed and reported. Ultrasonic irradiation technique was used as surface modification method to shorten the crosslinking reaction for hydrochar and polyethyleneimine (PEI). The PEI-USAH showed an excellent adsorption capacity for Cr(VI) from aqueous solution. The physicochemical properties of this PEI-modified adsorbent were comparatively characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis and CNHS analysis. The effects of contact time, initial pH, and biosorbent dose on adsorption capacities were investigated. The batch adsorption experiments showed that PEI-USAH possessed the maximum adsorption capacities of 94.38 mg/g and 330.84 mg/g for initial Cr(VI) concentration of 100 mg/L and 500 mg/L, respectively. Furthermore, this adsorption process could be fitted to Langmuir adsorption and described by the pseudo second order kinetic model. Based on the above findings, PEI-USAH could be used as a potential adsorbent for removal of Cr(VI) from wastewater.

Surface-modified spherical lignin particles with superior Cr(VI) removal efficiency

Lignin, natural aromatic polymer derived from plant dry matter, is second abundant biopolymer. Recently, interest in applications of lignin, especially as an adsorbent material is increasing. However, the physicochemical complexity of lignin significantly reduces access to practical environmental remediation processes. Also, there is a limitation because the adsorption performance of the pristine lignin materials is not superior to that of commercial adsorbent and ion exchange resin material. In this study, spherical lignin particles with high physicochemical stability and excellent Cr(VI) adsorption capacity are prepared using a polyethylenimine (PEI) modification strategy. This modification process significantly improves the mechanical properties and water stability of lignin by complementing the instability of lignin particles. In addition, the PEI-lignin particles exhibit a superior Cr(VI) removal capability (657.9 mg/g, the highest value for a PEI-modified natural adsorbent), which is attributed to their structural stability and introduced amine functional groups. The Cr(VI) removal with PEI-lignin particles is performed via intra-particle diffusion and adsorption followed by covalent bonding combined with a reduction process. Moreover, the PEI-lignin particles exhibit excellent reusability, which sustains their high adsorption efficiency over a long and repeated adsorption period. The results herein strongly support the potential use of PEI-lignin particles as a high performance bio-sorption material for heavy metal removal and its detoxification in aqueous wastewater streams. Evidently, this lignin-based bio-sorbent manufacturing system can provide sustainable bio-resource recycling and cost efficiency.

Enhanced adsorption-coupled reduction of hexavalent chromium by 2D poly(m-phenylenediamine)-functionalized reduction graphene oxide

To improve the mass transfer efficiency of poly(m-phenylenediamine) for the effective removal of hexavalent chromium (Cr (VI)) from aqueous solution, a facile and one-step method to prepare two-dimensional poly(m-phenylenediamine) functionalized reduction graphene oxide (rGO-PmPD) by dilution polymerization is developed. The structure and morphology of rGO-PmPD as well as rGO and PmPD were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), Fourier-transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD). The preparation mechanism, adsorption performance, and mechanism of rGO-PmPD were then investigated in detail. The obtained rGO-PmPD exhibited thin 2D nanosheet morphology with much improved specific surface area and pore volume (18 and 25 times higher than that of PmPD, respectively). The Cr (VI) adsorption of rGO-PmPD was fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum adsorption capacity of rGO-PmPD reached 588.26 mg g^-1, higher than that of PmPD (400 mg g^-1) and rGO (156.25 mg g^-1). Moreover, the regeneration efficiency of the rGO-PmPD nanosheet is also promising that the adsorption performance after five times of adsorption-desorption cycles still maintains more than 530 mg g^-1. The removal mechanism involved reduction coupled with adsorption and electrostatic interaction between rGO-PmPD and Cr (VI), and ~ 65% of Cr (VI) removal was attributed to reduction and ~ 35% was ascribed to adsorption and electrostatic interaction. This study thus provides a simple and effective route to achieve high accessible surface area of adsorbent materials with enhanced mass transfer efficiency and thereafter improved adsorption performance.

Ultrafast and efficient removal of anionic dyes from wastewater by polyethyleneimine-modified silica nanoparticles

Trace anionic dyes in wastewater are difficult to be rapidly and efficiently removed because they are completely soluble and poorly biodegradable. Herein, a facile and environmentally friendly adsorbent was fabricated via the surface functioned SiO₂ with abundant amine groups of polyethyleneimine (PEI). The structural characterization indicated that PEI was successfully immobilized on the SiO₂ surface. The adsorption performance of SiO₂-PEI was evaluated using acid orange II (AOII) as model pollutant. The adsorption of AOII on SiO₂-PEI displayed high removal rates in the pH range of 2.0-9.0, and exhibited ultrafast removal (99.1% removal rate at 10 min). The adsorption behavior fitted well with the Langmuir isotherm and pseudo-second-order kinetic model, and the maximum uptake capability of AOII was higher than 705.3 mg/g. The excellent adsorption capacity of AOII on SiO₂-PEI mainly relied on the electrostatic attraction between the sulfonic acid group of AOII and amine group of PEI in the adsorption process. Additionally, other anionic dyes like acid fuchsin and direct sky blue 5B could also be fast and efficiently removed by SiO₂-PEI. This work is expected to open new possibilities for the ultrafast removal of anionic dye pollutants.

A multi-functional-group modified cellulose for enhanced heavy metal cadmium adsorption: Performance and quantum chemical mechanism

Heavy metal contamination directly threatened human life and health. In this work, a novel carboxyl, amide, carbonyl sulfide and secondary amino group grafted cellulose derivative adsorbent (modified-cellulose) was prepared in an attempt to remove heavy metal Cd²⁺. The XRD, FTIR, ¹³C NMR and XPS results showed that the carboxyl, amide, carbonyl sulfide and secondary amino group were grafted onto the cellulose backbone successfully. Effects of various factors on the adsorption performance were investigated as well as the adsorption mechanism. The Cd²⁺ adsorption capacity of modified-cellulose was pretty good, up to 401.1 mg/g and with 3 times enhancement. The adsorption process was spontaneous, well described by the Freundlich model (R² = 0.994), confirmed to the pseudo-second-order model (R² > 0.997), and mainly controlled by chemisorption. The density functional theory (DFT) calculations indicating that the Cd²⁺ binding ability of multi-functional groups modified cellulose was stronger than that of single-functional group modified cellulose. The preferential adsorption sites were analyzed based on the frontier orbital theory (FOT), and they were concentrated on the secondary amino groups and carbonyl sulfides. It is foreseeable that the as-prepared modified-cellulose adsorbent has great potential in heavy metal cadmium removal, and our conclusions could provide significant theoretical guidance in the due bioresource utilization.

Hydrophobic IR780 loaded sericin nanomicelles for phototherapy with enhanced antitumor efficiency

The near-infrared dye, IR780 iodide, has been utilized in photodynamic therapy (PDT) and photothermal therapy (PTT). However, the hydrophobicity and photosensitivity of IR780 limit its further applications in biomedical fields. Herein, the hydrophilic sericin was modified with hydrophobic cholesterol to form an amphiphilic macromolecular conjugate (Ser-Chol). The tumor-targeting agent, folic acid (FA), was further linked to the conjugate (FA-Ser-Chol). The IR780 could be encapsulated into such amphiphilic macromolecule to form stable micelles (FA-Ser-Chol/IR780) by self-assembly, and the solubility and photo-stability of IR780 were greatly improved. The FA-Ser-Chol/IR780 micelles could be efficiently absorbed by FA-positive gastric cancer cells (BGC-823) through FA receptors, while the uptake micelles showed remarkable PDT and PTT cytotoxicity towards BGC-823 cells under laser irradiation of 808 nm. Therefore, FA-Ser-Chol micelles may serve as a promising IR780 carrier for PDT and PTT therapy.

Hexavalent chromium ion and methyl orange dye uptake via a silk protein sericin-chitosan conjugate

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan-sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange (MO) dye from aqueous solutions. The CS was shown to effectively remove Cr(vi) ions and MO dye at maximum adsorption capacities (Langmuir) of 139 mg g-1 for Cr(vi) ions and 385 mg g-1 for MO dye. Moreover, the adsorption of both Cr(vi) ions and MO dye was highly pH dependent and varied under different experimental conditions. Cr(vi) ion and MO dye uptake by the CS was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry analysis. Additionally, XPS analysis of the Cr(vi)-loaded CS revealed that Cr(vi) was reduced to the less toxic Cr(iii). The CS was shown not only to be highly amenable to regeneration, but also to be able to effectively remove MO dye and Cr(vi) ions from a binary mixture.