Fabrication and characterization of chitosan-crosslinked-poly(alginic acid) nanohydrogel for adsorptive removal of Cr(VI) metal ion from aqueous medium

Synthesis of fenugreek gum-based metal-organic framework (FG/Zr-AIPA MOF) composite beads for sequestration of heavy metal ions from aqueous solution

Metal-organic frameworks (MOFs) are a prominent class of materials due to their large surface area and customized structures. This gives them specificity and high adsorption capacity while they lack mechanical strength and reusability. Integrating MOFs with polysaccharide matrix may retain MOF characteristics along with imparting structural integrity. In the present study, zirconium MOF-based fenugreek composite (FG/Zr-AIPA) beads were synthesised by a single droplet method and utilised for removal of Cr(VI), Pb(II) and Fe(III) from aqueous solution. The structure, morphology and composition of beads were evaluated by FTIR, XRD, TGA, BET, FESEM, EDX, XPS and zeta potential analysis. Adsorption isotherm, kinetics and thermodynamics were studied for Cr(VI), Pb(II) and Fe(III) adsorption. Adsorption kinetics and isotherm study revealed that all the metal ions were adsorbed through a monolayer chemisorption process. The maximum adsorption capacity was 344.43, 270.02 and 223.21 mg g-1 for Cr(VI), Pb(II) and Fe(III), respectively, based on the Langmuir isotherm study. The thermodynamics study revealed that the interaction between the metal ions and the composite beads was spontaneous and endothermic. The FG/Zr-AIPA composite beads exhibited good reusability for the removal of Cr(VI), Pb(II) and Fe(III). The results open new possibilities for the preparation of polysaccharide MOF-based composite beads which exhibit substantial potential for water treatment applications.

Synergistic adsorption of methylene blue with carrageenan/hydrochar-derived activated carbon hydrogel composites: Insights and optimization strategies

The study explores the use of hydrochar-derived activated carbon (AC) to improve the adsorption capacity and mechanical properties of carrageenan (CAR) hydrogel beads. Four distinct samples, with carrageenan to activated carbon ratios of 1:0 (CAR), 2:1 (CAC2), 4:1 (CAC4), and 10:1 (CAC10), were prepared. These polymeric beads underwent comprehensive evaluation for their methylene blue (MB) adsorption capacity, gel content (GC), and swelling ratio (SR). Increasing activated carbon content up to 50 % of carrageenan mass significantly enhanced GC and SR by 20.57 % and 429.24 %, respectively. Various analytical techniques were employed to characterize the composites, including FTIR, XRD, Raman Spectroscopy, BET, SEM, and EDS-Mapping. Batch adsorption tests investigated the effects of pH, contact time, dye concentration, and temperature on MB adsorption. Maximum adsorption capacities for CAR, CAC10, CAC4, and CAC2 were 475.48, 558.54, 635.93, and 552.35 mg/g, respectively, under optimal conditions. Kinetic models (Elovich and pseudo-second-order) and isotherm models (Temkin for CAR and Freundlich for CAC10, CAC4, and CAC2) fitted well with the experimental data. Thermodynamic analysis showed spontaneous, exothermic MB adsorption. Primary mechanisms include electrostatic attraction, hydrogen bonding, n-π, and π-π stacking. The study highlights enhanced adsorption capacity of carrageenan hydrogel via carrageenan/activated carbon composites, providing cost-effective wastewater treatment.

Effective removal of Allura red food dye from water using cross-linked chitosan-diatomite composite beads

Chitosan (Ch)-diatomite (D) composite beads (Ch-D) were synthesized using epichlorohydrin and tripolyphosphate crosslinkers and then moulded into uniform beads in tripolyphosphate solution. FT-IR and SEM-EDX analyses showed that Ch-D composite adsorbent was successfully synthesized by functionalization of chitosan to Ch-D by hydrogen bonding and electrostatic interactions and improved adsorption capacity for removal of Allura red AC (AR) food dye. The removal rate of AR food dye was found to be 98 % at 25 °C, natural AR dye pH value, 24 h, and at the initial AR dye concentration of 200 mg L-1. The maximum adsorption capacity was found to be 34.7 mg g-1. It was observed that π-π interactions, hydrogen bonds, and electrostatic interactions between the functional groups containing oxygen and amine on the surface of the Ch-D composite and the functional groups of the anionic AR dye, and AR dye adsorption via complexation took place. In light of all this information, the Ch-D composite adsorbent is a promising potential material for the effective treatment of colored pollutants from wastewater.

Removal of nafcillin from aqueous solution with green synthesis iron oxide nanoparticles

In this study, iron oxide nanoparticles were synthesized from Solanum nigrum L. extract and used to remove nafcillin, which exhibits toxic properties in aqueous solutions. To understand the adsorption behavior of naphcillin on the nanoadsorbent, the optimum conditions, kinetics and isotherm of adsorption were studied in detail. It was found that the adsorption process was consistent with the pseudo-second order kinetic model and Langmuir's isothermal model. The FeONPs adsorbent achieved an adsorption capacity of 116.3 mg/g for nafcillin. It was also found that FeONPs retained ~90% of its adsorption capacity after five adsorption-desorption cycles. Apart from the fact that the nanoparticles synthesized in the study are composed of natural ingredients, S. nigrum L. which causes problems in plant cultivation, serves a useful purpose by being used in this method. The results show that this new nanoadsorbent provides an alternative option for the removal of pharmaceuticals and various pollutants in wastewater.

Effective removal of Cr (VI) from aqueous solution by reinforced sodium alginate/polyethyleneimine/graphene oxide composite aerogels

A reinforced composite aerogel absorbent was synthesized using a green chemistry method and an environmentally friendly freeze-drying technique. The absorbent consisted of sodium alginate, polyethyleneimine (PEI), and graphene oxide (GO). The ability of the absorbent to remove Cr (VI) ions from aqueous solutions was studied. PEI was a nitrogen source for Cr (VI) removal and a cross-linking agent for GO sheets, while SA was a reinforcing material. The aerogel was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, texture analysis, Raman spectroscopy, and thermogravimetric analysis (TGA). Batch studies were conducted to investigate the effect of pH and contact time on adsorption. The results indicated that the SA/PEI/GO aerogel had a maximum adsorption capacity of 174.05 mg·g-1 for Cr (VI) at pH 2. The adsorption mechanism was described using the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. The aerogel demonstrated good regeneration ability and satisfactory recovery for Cr (VI) even after five cycles. These findings suggest that the composite aerogel could be a promising adsorbent for efficiently removing Cr (VI) from wastewater.

Efficient Removal of Heavy Metals from Aqueous Solution Using Licorice Residue-Based Hydrogel Adsorbent

The removal of heavy metals through adsorption represents a highly promising method. This study focuses on the utilization of an abundant cellulose-rich solid waste, licorice residue (LR), as a natural material for hydrogel synthesis. To this end, LR-EPI hydrogels, namely, LR-EPI-5, LR-EPI-6 and LR-EPI-8, were developed by crosslinking LR with epichlorohydrin (EPI), specifically targeting the removal of Pb, Cu, and Cr from aqueous solutions. Thorough characterizations employing Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy confirmed the successful crosslinking of LR-EPIs by EPI, resulting in the formation of porous and loosely structured hydrogels. Batch studies demonstrated the high efficacy of LR-EPI hydrogels in removing the three heavy metal ions from aqueous solutions. Notably, LR-EPI-8 exhibited the highest adsorption capacity, with maximum capacities of 591.8 mg/g, 458.3 mg/g, and 121.4 mg/g for Pb²⁺, Cr³⁺, and Cu²⁺, respectively. The adsorption processes for Pb²⁺ and Cu²⁺ were well described by pseudo-second-order kinetics and the Langmuir model. The adsorption mechanism of LR-EPI-8 onto heavy metal ions was found to involve a combination of ion-exchange and electrostatic interactions, as inferred from the results obtained through X-ray photoelectron spectroscopy and FTIR. This research establishes LR-EPI-8 as a promising adsorbent for the effective removal of heavy metal ions from aqueous solutions, offering an eco-friendly approach for heavy metal removal and providing an environmentally sustainable method for the reutilization of Chinese herb residues. It contributes to the goal of "from waste, treats waste" while also addressing the broader need for heavy metal remediation.

Structural regulatory mechanism of phosphotungstate acid decorated graphene oxide quantum dots-chitosan aerogel and its application in ciprofloxacin degradation

Chitosan modified AGQD (amine modified graphene oxide quantum dots) and then combined with H₃PW₁₂O₄₀ to obtain CS_x@AGQD-HPW₁₂ via facile process and applied for CIP removal through pre-adsorption and photocatalytic processes. The application of chitosan could regulate the morphology and photoelectric properties effectively. CS_0.5@AGQD-HPW₁₂ was found to have the optimal CIP removal performance among all the products, the corresponding adsorption removal efficiency and pre-adsorption photocatalysis process were 72.1 % and 98.8 %, respectively. Results of toxicity assessment confirmed photocatalytic degradation process could mitigate the ecotoxicity of CIP effectively. The optimal TOC (total organic carbon) removal efficiency was about 52.1 %. Possible pathways for CIP degradation and reaction mechanism were proposed based on the results of intermediates analysis and trapping experiments. This demonstrated a novel approach to chitosan application and an eco-friendly way to remove CIP by adsorption-photocatalysis process.

Zr4+ and glutaraldehyde cross-linked polyethyleneimine functionalized chitosan composite: Synthesis, characterization, Cr(VI) adsorption performance, mechanism and regeneration

In order to improve the stability, electrostatic interaction and ion exchange ability of chitosan for Cr (VI) removal, it is an effective strategy to introduce polyvalent metal ions and polymers into chitosan molecular chain through crosslinking. In this paper, Zr⁴⁺ and glutaraldehyde crosslinked polyethyleneimine functionalized chitosan (CGPZ) composite was successfully synthesized and characterized by XRD, SEM, FTIR, BET, and XPS. The results showed that polyethyleneimine was successfully grafted onto chitosan by Schiff base reaction, while the appearance of ZrO and ZrN bonds verified the successful preparation of CGPZ. The monolayer maximum adsorption capacity of Cr(VI) by CGPZ was 593.72 mg g^-1 at 298 K and t = 210 min. The removal efficiency of 100 mg L^-1 Cr(VI) reached 95.7 %. The thermodynamic, isotherm and kinetic results show that the adsorption process of Cr (VI) by CGPZ is a spontaneous endothermic process controlled by entropy, which accords with Freundlich model and pseudo-second-order kinetic model. The regeneration experiments show that both HCl and NaOH can effectively desorb Cr(III) and Cr(VI) from the adsorbent surface, and the adsorbent has good acid-base resistance and regeneration performance. The removal of Cr(VI) mainly involves electrostatic attraction, ion exchange, reduction and complexation. CGPZ can synergistically adsorb Cr(VI) by electrostatic interaction of -NH₂/-C=N and ion exchange of Cl^- ion in the center of Zr, then reduce Cr(VI) to Cr(III) (45.4 % at pH = 2.0) by the -OH group on its surface, and chelate Cr(III) through COO- and -NH- groups.

Selective removal of heavy metals by Zr-based MOFs in wastewater: New acid and amino functionalization strategy

Zr-based metal-organic frameworks (MOFs) have been developed in recent years to treat heavy metals, e.g. hexavalent chromium Cr⁶⁺ pollution, which damages the surrounding ecosystem and threaten human health. This kind of MOF is stable and convenient to prepare, but has the disadvantage of low adsorption capacity, limiting its wide application. To this end, a novel formic acid and amino modified MOFs were prepared, referred to as Form-UiO-66-NH₂. Due to the modification of formic acid, its specific surface area, pore size, and crystal size were effectively expanded, and the adsorption capacity of Cr⁶⁺ was significantly enhanced. Under optimal conditions, Form-UiO-66-NH₂ exhibited an excellent adsorption capacity (338.98 mg/g), ∼10 times higher than that reported for unmodified Zr-based MOFs and most other adsorbents. An in-depth study on the photoelectronic properties and pH confirmed that the adsorption mechanism of Form-UiO-66-NH₂ to Cr⁶⁺ was electrostatic adsorption. After modification, the improvement of Cr⁶⁺ adsorption capacity by Form-UiO-66-NH₂ was attributed to the expansion of its specific surface area and the increase in its surface charge. The present study revealed an important finding that Form-UiO-66-NH₂ elucidated selective adsorption to Cr⁶⁺ in mixed wastewater containing toxic heavy metal ions and common nonmetallic water quality factors. This research provided a new acid and amino functionalization perspective for improving the adsorption capacity of Zr-based MOF adsorbents while simultaneously demonstrating their pertinence to target contaminant adsorption.

Green synthesis of ceramsite from industrial wastes and its application in selective adsorption: Performance and mechanism

The increasing requirement and consumption of coal has resulted in a large accumulation of coal gangue. The reuse and recycling of coal gangue have become a high priority for sustainable development. A sustainable and efficient ceramsite adsorbent was prepared for copper ions adsorption by using coal gangue, coal fly ash, and copper slag as the main materials. The appropriate performance of the ceramsite could be obtained at a mixture of coal gangue, coal fly ash, and copper slag at a weight ratio of 3:4:1. The optimal sintering temperature and time were 1050 °C and 20 min, respectively. The main crystalline phases of ceramsite were quartz, mullite, and anorthite. Many micropores are connecting the interior on the surface of ceramsite under scanning electron microscope. The maximum copper ions adsorption capacity reached up to 20.6 mg/g at 303 K when pH and time were 5 and 1440 min, respectively. The adsorption kinetics and isotherm could be described by the pseudo-second-order model and Freundlich model, respectively. The adsorption mechanisms of Cu²⁺ with ceramsite were attributed to Cu(OH)₂ precipitation formed on the alkaline surface of ceramsite and complexation reactions occurred between the O-containing groups (including C-O, Fe-O, and Si-O) from ceramsite and Cu²⁺. The prepared ceramsite may be also applied to other heavy metal wastewater treatments.

Glutaraldehyde base-cross-linked chitosan-silanol/Fe3O4 composite for removal of heavy metals and bacteria

We designed and synthesised a magnetic adsorbent (Fe₃O₄@Si-OH@CS-Glu) combining chitosan-silanol groups with glutaraldehyde as a cross-linking agent, which has improved physicochemical properties and can be used to remove multiple heavy metals and bacteria from polluted water. The adsorbent was characterised with SEM, XRD, FTIR, BET, VSM, and zeta potential. Under optimum conditions, the adsorption efficiencies of Fe₃O₄@Si-OH@CS-Glu for Cr⁶⁺, As⁵⁺, Hg²⁺, and Se⁶⁺ were as high as 90.5%, 73.5%, 91.6%, and 100% respectively. In addition, Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) can be removed after 2-4 adsorption cycles with 2.5 mg Fe₃O₄@Si-OH@CS-Glu. The main adsorption mechanism of the adsorbent for heavy metals and bacteria is electrostatic adsorption. Overall, the synthesised Fe₃O₄@Si-OH@CS-Glu adsorbent showed high removal efficiency and adsorption capacity with a stable structure and easy separation. It has promising applications for the removal of heavy metals and bacteria from water.

Quantitative assessment and optimization of bi-functional membrane for remediation of Cr(VI) from wastewater

This paper explores the innovative approach of using a green route synthesized cost-effective bi-functional to eliminate toxic hexavalent chromium commonly found in tannery wastewater by using an integrated application of membrane and photocatalyst. Contaminated wastewater is firstly passed through bi-functional ultrafiltration membranes to retain hexavalent chromium and further reducing the toxicity of rejected water having high concentrations of Cr(VI) by photocatalytic reduction into Cr(III) in the presence of sunlight using the same membrane as photocatalyst film. Conditions governing the separation process such as solution pH, nanoparticle loading in polymer matrix, and concentration of Cr(VI) have been optimized to maximize the % rejection and photocatalytic reduction to Cr(III). The purpose of this work was to optimize the process condition through the use of the response surface method (RSM) that governs the process. RSM analysis concludes that excellent rejection of 91.58% and reduction of 87.02% is possible at the predicted pH (5.55), particle loading (2.14%) and Cr(VI) concentration (25 mg/L).

New alginic acid derivatives ester for methylene blue dye adsorption: kinetic, isotherm, thermodynamic, and mechanism study

In this paper, the application of ester materials prepared by grafting different carbon chain lengths of diols in alginic acid (AA) by a simple, fast and efficient method for the adsorption of methylene blue (MB) is studied. The AA ester derivatives are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Zeta potential before and after MB adsorption. This study shows a significant improvement in the adsorption capacity of MB by AA after its esterification with a Q_max value up to 454.545 mg/g for the best adsorbent "Poly(AA-g-EG)". The experimental data are studied according to two isothermal models (Langmuir and Freundlich) and two kinetic models (pseudo-second order and intra-particle diffusion). The adsorption of MB is also evaluated thermodynamically. An adsorption mechanism of MB is established.

Sugarcane cellulose-based composite hydrogel enhanced by g-C3N4 nanosheet for selective removal of organic dyes from water

The effective removal of toxic dyes from aqueous solution is of great significance for environmental protection. Herein, an eco-friendly sugarcane cellulose (SBC)/sodium carboxymethylcellulose (CMC-Na) adsorbent reinforced with carbon nitride (g-C₃N₄) was successfully prepared via a facile sol-gel method. The resulting gel-like adsorbent or composite hydrogel was comprehensively characterized with FTIR, SEM, EDS, TGA analysis. The adsorption behaviors of the adsorbent in the removal of methylene blue (MB) were systematically investigated. Results showed the pseudo-second-order kinetic model and Langmuir model described adsorption process accurately with the maximum adsorption capacity of 362.3 mg g^-1, indicating that adsorption behavior is a monolayer chemical adsorption. Moreover, the composited hydrogel displayed excellent adsorption selectivity on MB/MO or MB/RhB mixed dyes. In addition, adsorbent showed great stability and reusability with almost no loss in adsorption capacity after 7 cycles. Due to the facile preparation process and outstanding mechanical properties, as well as high recyclability, g-C₃N₄@SBC/CMC has great potential in wastewater treatment.

Chitosan as a Tool for Sustainable Development: A Mini Review

New developments require innovative ecofriendly materials defined by their biocompatibility, biodegradability, and versatility. For that reason, the scientific society is focused on biopolymers such as chitosan, which is the second most abundant in the world after cellulose. These new materials should show good properties in terms of sustainability, circularity, and energy consumption during industrial applications. The idea is to replace traditional raw materials with new ecofriendly materials which contribute to keeping a high production rate but also reducing its environmental impact and the costs. The chitosan shows interesting and unique properties, thus it can be used for different purposes which contributes to the design and development of sustainable novel materials. This helps in promoting sustainability through the use of chitosan and diverse materials based on it. For example, it is a good sustainable alternative for food packaging or it can be used for sustainable agriculture. The chitosan can also reduce the pollution of other industrial processes such as paper production. This mini review collects some of the most important advances for the sustainable use of chitosan for promoting circular economy. Hence, the present review focuses on different aspects of chitosan from its synthesis to multiple applications.

Gum Acacia-Crosslinked-Poly(Acrylamide) Hydrogel Supported C3N4/BiOI Heterostructure for Remediation of Noxious Crystal Violet Dye

Herein, we report the designing of a C₃N₄/BiOI heterostructure that is supported on gum acacia-crosslinked-poly(acrylamide) hydrogel to fabricate a novel nanocomposite hydrogel. The potential application of the obtained nanocomposite hydrogel to remediate crystal violet dye (CVD) in an aqueous solution was explored. The structural and functional analysis of the nanocomposite hydrogel was performed by FTIR (Fourier transform infrared spectroscopy), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The different reaction parameters, such as CVD concentration, nanocomposite hydrogel dosage, and working pH, were optimized. The C₃N₄/BiOI heterostructure of the nanocomposite hydrogel depicts Z-scheme as the potential photocatalytic mechanism for the photodegradation of CVD. The degradation of CVD was also specified in terms of COD and HR-MS analysis was carried to demonstrate the major degradation pathways.

Activated Carbon as Superadsorbent and Sustainable Material for Diverse Applications

Activated carbon is a carbonaceous material with highly porous structure. Different functionalities can be introduced to its surface by various physical and chemical treatments. Various precursors can be used for the synthesis of activated carbon such as fossil fuels, agricultural wastes, and lignocellulosic wastes, etc. Number of papers have been reported in literature devoted to the synthesis, characterization, and various applications of activated carbon. Herein, in this review, special attention has been paid to the basic properties of activated carbon and its surface chemistry originated due to physical and chemical treatment. In addition, a general introduction to adsorption process, various adsorption isotherms, and adsorption kinetics is also included. A brief description of mechanism of adsorption onto activated carbon is also presented. At last, most probable applications of activated carbon such as adsorption of pollutants (e.g., dyes, heavy metal ions, pesticides, pharmaceutical waste products, and volatile organic organic), as catalyst support, anduse in food and pharmaceutical industries is also presented.

A novel environmentally friendly nanocomposite aerogel based on the semi-interpenetrating network of polyacrylic acid into Xanthan gum containing hydroxyapatite for efficient removal of methylene blue from wastewater

Eco-friendly nanocomposite aerogels were prepared as adsorbents for the removal of a model pollutant (methylene blue, MB) from water. These aerogels were comprised of hydroxyapatite (HA) nanoparticles embedded within a polymer matrix consisting of a semi-interpenetrating network of xanthan gum (XG) and polyacrylic acid (PAA). Microscopy and BET analysis showed that the aerogels formed had a nanofibrous porous microstructure with a surface area of 89 m²/g. Rheological analysis showed that the aerogels were viscoelastic materials whose elasticity increased with increasing HA concentration (up to 5 w/w%). The aerogels were effective at removing MB from water, exhibiting an adsorption capacity of 130 mg/g after 200 min. The binding of the MB to the aerogels was mainly attributed to hydrogen bonding and electrostatic attraction. A reusability test showed that the MB removal efficiency of over 86% was preserved after 10 cycles of adsorption-desorption. These results suggest that our nanocomposite aerogels may be useful for the efficient removal of anionic pollutants from wastewater and water supplies due to their ease of synthesis, cost-effectiveness, good mechanical properties, high thermal stability, and good adsorption performance.

Visible-light-driven sonophotocatalysis for enhanced Cr(VI) reduction based on mixed-linker zirconium-porphyrin MOFs

In this study, we synthesized and characterized two mixed-linker zirconium-porphyrin metal-organic frameworks, PCN-134 and PCN-138 which constructed from tetratopic light harvesting TCPP ligand and tritopic BTB/TBTB ligand (TCPP = trakis(4-carboxyphenyl)porphyrin),...

Synthesis of tri-metallic surface engineered nanobiochar from cynodon dactylon residues in a single step - Batch and column studies for the removal of copper and lead ions

Superparamagnetic nanocomposites integrated with multiple metals, and surface engineered nanoparticles play a vital role in the removal of heavy metals. In the present study, amino-functional silica-coated magnetic nanocomposites with biochar synthesised from Cynodon dactylon plant residues are prepared in a single step reaction process. The synthesised nanocomposites are characterized using various analytical techniques such as FTIR to determine their functional entities, SEM, TEM, EDX and VSM to analyse the size (~50 nm), elements and magnetic nature of the nanocomposites. Characterization reveals that the prepared nanobiochar was coated with silica and a specific amine group. The magnetic saturation value of 50 emu/g confirms the prepared sorbent was superparamagnetic. Kinetics, isotherm and thermodynamics parameters are evaluated to study the metal interaction mechanism with the nanocomposites where the system follows pseudo-second-order kinetics and the four-parameter Fritz Schlunder model for both metal ions. The nanocomposites showed the enhanced adsorption capacity of copper (Cu(II)) ions with 220.4 mg/g and 185.4 mg/g for lead (Pb(II)) ions. The nanocomposites also showed the excessive reusing ability of 15 times with the maximum removal efficiency for Cu(II) and Pb(II) metal ions. Column studies are evaluated to demonstrate the vital performance in the removal of Cu(II) ions and the breakthrough point was inferred for the parameters such as concentration (100-300 mg/L), bed height (1-3 cm) and flow rate (2-4 mL/min). The breakthrough point was attained at 1400 min and the removal efficiency of about 64.58% was obtained.

Visible-Light-Driven Sonophotocatalysis for the Rapid Reduction of Aqueous Cr(VI) Based on Zirconium-Porphyrin Metal-Organic Frameworks with csq Topology

Photochemical treatment of highly toxic Cr(VI) is a desirable and ecofriendly method to protect the environment and human beings. In this study, a MOF-based sonophotocatalytic system is established, in which visible-light-driven sonophotocatalytic reduction of toxic Cr(VI) to Cr(III) in water is investigated using zirconium-porphyrin metal-organic frameworks (MOFs) structured as PCN-222(M) [M = H₂, Zn(II), Fe(III), Co(II)]. In the view of the synergistic effect of sonochemistry and photocatalysis, PCN-222(M) exhibited enhanced activities for Cr(VI) reduction compared with the photocatalytic process. Kinetic studies showed that apparent reaction rate constants in the sonophotocatalytic system of PCN-222(M) are 1.5-3.3 times higher than those in photocatalysis. Fluorescence and UV-vis absorption spectra measurements demonstrate that the sonophotocatalytic process promotes the transfer of photoinduced electrons from PCN-222(M) to Cr(VI), thus enhancing the catalytic performance. The innovative combination of porous MOFs and sonophotocatalytic technology might become a feasible strategy to improve the existing MOF-based photocatalytic systems.

Chitosan-based recyclable composite aerogels for the photocatalytic degradation of rhodamine B

TiO₂ based photocatalyst with sufficient reusability for the degradation of water pollutants remains a challenge. Here, we report a composite chitosan-based aerogel containing TiO₂ nanoparticles, multiwalled carbon nanotubes and layered silicate rectorite with sufficient mechanical strength for Rhodamine B degradation. The aerogels with homogeneous oriented lamellar structure were successfully prepared via a unidirectional freeze-casting technique. As-prepared aerogels showed specific surface area of 84.59 m²/g. The addition of rectorite and carbon nanotubes accelerated the photodegradation and rectorite significantly enhanced the overall mechanical performance. Rapid degradation of rhodamine B (95% in 100 min) was observed on aerogels with 2 wt% and 4 wt% of rectorite. After 3 cycles, 75% degradation of Rhodamine B was achieved with CTCR4, confirming its reusability. Thus, the composite chitosan aerogels show high photocatalytic degradation efficiency towards Rhodamine B during cycle use.

Removal of Zn(II) and Ni(II) heavy metal ions by new alginic acid-ester derivatives materials

The present work concerns the preparation of new materials based on alginic acid (AA) and diols in a facile and efficient process by improving the adsorption properties of Zn(II) and Ni(II) metal ions on the modified AA. The materials were analysed by zeta potential, thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), in addition to the Fourier Transform InfraRed spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) before and after the adsorption behaviour was conducted. The results show that the esterification of AA with diols of different lengths significantly improves its adsorption efficiency of Zn(II) and Ni(II) with Q_max up to 200 mg/g and 185.185 mg/g respectively. Equilibrium and kinetic studies showed that the Langmuir and Freundlich adsorption isotherm models fit the experimental data well, and followed a pseudo-first order kinetic model and the particle diffusion model with correlation coefficients R² ≈ 1.

Synthesis, Characterization and Application of Polypyrrole Functionalized Nanocellulose for the Removal of Cr(VI) from Aqueous Solution

Heavy metals are toxic substances that pose a real danger to humans and organisms, even at low concentration. Therefore, there is an urgent need to remove heavy metals. Herein, the nanocellulose (NC) was synthesized by the hydrolysis of cellulose using sulfuric acid, and then functionalized using polypyrrole (ppy) through a polymerization reaction to produce polypyrrole/nanocellulose (ppy/NC) nanocomposite. The synthesized nanocomposite was characterized using familiar techniques including XRD, FT-IR, SEM, TEM, and TGA. The obtained results showed a well-constructed nanocomposite with excellent thermal stability in the nano-sized scale. The adsorption experiments showed that the ppy/NC nanocomposite was able to adsorb hexavalent chromium (Cr(VI)). The optimum pH for the removal of the heavy metal was pH 2. The interfering ions showed minor effect on the adsorption of Cr(VI) resulted from the competition between ions for the adsorption sites. The adsorption kinetics were studied using pseudo 1st order and pseudo 2nd order models indicating that the pseudo second order model showed the best fit to the experimental data, signifying that the adsorption process is controlled by the chemisorption mechanism. Additionally, the nanocomposite showed a maximum adsorption capacity of 560 mg/g according to Langmuir isotherm. The study of the removal mechanism showed that Cr(VI) ions were removed via the reduction of high toxic Cr(VI) to lower toxic Cr(III) and the electrostatic attraction between protonated ppy and Cr(VI). Interestingly, the ppy/NC nanocomposite was reused for Cr(VI) uptake up to six cycles showing excellent regeneration results. Subsequently, Cr(VI) ions can be effectively removed from aqueous solution using the synthesized nanocomposite as reusable and cost-effective adsorbent.

Adsorption behavior and mechanism of Serratia marcescens for Eu(III) in rare earth wastewater

Directly discharging low-concentration rare-earth wastewater not only wastes rare-earth resources but also pollutes the environment. In this study, the biosorption behavior of Serratia marcescens for Eu(III) was studied with emphasis on the optimization of adsorption conditions, adsorption kinetics, and adsorption isotherm. It was shown that the maximum adsorption capacity of Serratia marcescens reached 115.36 mg·g^-1 under an optimal condition, indicating the good adsorption capability of Serratia marcescens for Eu(III). The adsorption kinetics and adsorption isotherm analysis showed that the adsorption process conforms to the pseudo-second-order kinetic model and Langmuir adsorption isotherm, indicating that the adsorption of Eu(III) by Serratia marcescens is a monolayer chemical adsorption process. In addition, the adsorption mechanism was investigated by using characterizations of zeta potential, scanning electron microscope-energy dispersive spectrometer (SEM-EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. It was revealed that the adsorption of Eu(III) by S. marcescens is a combination of electrostatic attraction, ions exchange and coordination. These findings indicate that S. marcescens can be used as a potential biosorbent to recover rare earth elements from rare earth wastewater.

Trimetallic@Cyclodextrin Nanocomposite: Photocatalyst for Degradation of Amoxicillin and Catalyst for Esterification Reactions

The industry is looking for new materials which can respond to specific applications that exclusively advance materials can provide. In this context, nanoparticles and nanocomposites opened an interesting method for designing specific properties which can be modulated according to the requirements. The preparation of biomolecules supported trimetallic nanoparticles and some other derives is a good example of the complex systems that can be designed for getting exclusive properties. This study is based on the preparation of new cyclodextrin supported Fe/La/Zn trimetallic nanocomposite by the microemulsion technique. Photocatalytic degradation of amoxicillin was performed using cyclodextrin-Fe/La/Zn. 78% of amoxicillin photodegradation along 4 hours of photoirradiation was achieved. Finally, the catalytic nature of new material was explored for oxidation and esterification reactions. The present study revealed that this advanced multifunctional nanomaterial can be successfully employed for environmental remediation and catalytic activities.

Novel green strategy for CuO-ZnO-C nanocomposites fabrication using marigold (Tagetes spp.) flower petals extract with and without CTAB treatment for adsorption of Cr(VI) and Congo red dye

The CuO-ZnO-Carbon (CZC) nanocomposites (NCs) were synthesized via a green method at 300 and 400 °C calcinated temperatures, using waste marigold (Tagetes spp.) flower petal extract as a reducing agent and carbon source. A novel green strategy for the synthesis of highly effective CZC NCs was developed which showed better adsorption of toxic Cr(VI) and Congo red (CR) dye compared to unsupported carbon NCs. In this strategy, fine powder of petals as carbon source were passed with the flower liquid extract during the filtration process, which supported the metal oxides nanorods(NRs)/nanoparticles(NPs) on the surface. Furthermore, the surface of the synthesized NCs was modified by Cetyl Trimethyl Ammonium Bromide (CTAB) cationic surfactant to increase surface functionality, surface area, and positive charge density of NCs. Additionally, the adsorption performance of Cr(VI) and CR dye improved from acidic pH to neutral pH after surfactant modification of NCs compared to unmodified NCs. The characterization techniques such as Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, Point of zero charge (pHpzc), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were performed to examine physio-chemical properties of NCs and CTAB modified NCs. The FTIR and BET analysis confirmed that CTAB modified NCs showed excellent functionality and more than 49% and ~67% greater surface area than CZC-300 and CZC-400, respectively, which prepared at 300 and 400 °C temperature. XRD analysis confirmed that NCs were highly crystalline and no phase change after surfactant modification. The FE-SEM and TEM analysis confirmed the pentagonal NRs and spherical NPs of ZnO and CuO, respectively, were formed on the carbon surface. After CTAB modification, no change in the surface morphology of NCs was observed. Thus, comparative study of NCs and CTAB modified NCs was done for Cr(VI) and CR dye adsorption by varying batch conditions, such as initial pH, contact time, temperature, and initial concentration of Cr(VI)/CR dye. The equilibrium time and concentration data were fitted with non-linear forms of kinetic and isotherm models, respectively. CTAB modified CZC-300 NCs showed excellent adsorption capacity for both pollutants up to pH 6 compared to CZC-300 and CZC-400 NCs. Additionally, the maximum adsorption capacity of CTAB modified NCs for Cr(VI) and CR dye were 201.56 and 331.36 mg/g, respectively, at pH 2 and 30 °C and increased with increasing temperature. The effect of co-existing anions on adsorption capacity of both NCs for Cr(VI) and CR dye adsorption was investigated. The regeneration and reusability experiments of both NCs were also performed.

Adsorption/desorption performance of Pb2+ and Cd2+ with super adsorption capacity of PASP/CMS hydrogel

Super-absorbent polyaspartic acid/carboxymethyl Salix psammophila powder (PASP/CMS) hydrogel was prepared by aqueous solution polymerization. PASP/CMS hydrogel was characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that PASP/CMS hydrogel is prepared by graft copolymerization of the -COOH of polyaspartic acid (PASP) and the -CH₂OH of CMS. The surface of the hydrogel became dense from loose porosity, and Pb²⁺ and Cd²⁺ were adsorbed onto the surface of hydrogel. The crystallinity of CMS was destroyed by the addition of PASP. The initial concentration of Pb²⁺ and Cd²⁺, pH, adsorption time and adsorption temperature on the adsorption effect were studied through experiments. Results showed that hydrogel has a good removal effect on Pb(II) and Cd(II) ions. Pseudo-second-order kinetics and Langmuir isotherm models are represented in the process, which are spontaneous, exothermic and decreased in randomness, and it is a single layer chemical adsorption. At the same time, the effect of desorption experimental parameters (HNO₃ initial concentration, desorption time, and desorption temperature) on the experiment was studied and optimized.

Carbon-based adsorbents for fluoroquinolone removal from water and wastewater: A critical review

This review summarizes the adsorptive removal of Fluoroquinolones (FQ) from water and wastewater. The influence of different physicochemical parameters on the adsorptive removal of FQ-based compounds is detailed. Further, the mechanisms involved in the adsorption of FQ-based antibiotics on various adsorbents are succinctly described. As the first of its kind, this paper emphasizes the performance of each adsorbent for FQ-type antibiotic removal based on partition coefficients of the adsorbents that is a more sensitive parameter than adsorption capacity for comparing the performances of adsorbents under various adsorbate concentrations and heterogeneous environmental conditions. It was found that π-π electron donor-acceptor interactions, electrostatic interactions, and pore-filling were the most prominent mechanisms for FQ adsorption by carbon and clay-based adsorbents. Among all the categories of adsorbents reviewed, graphene showed the highest performance for the removal of FQ antibiotics from water and wastewater. Based on the current state of knowledge, this review fills the gap through methodolically understanding the mechanism for further improvement of FQ antibiotics adsorption performance from water and wastewater.

Hexavalent Cr ion adsorption and desorption behaviour of expanded poly(tetrafluoro)ethylene films grafted with 2-(dimethylamino)ethyl methacrylate

A new polymeric adsorbent for Cr(VI) ions based on an expanded poly(tetrafluoroethylene) (ePTFE) film was prepared by the combined use of the pretreatment with oxygen plasma and photografting of 2-(dimethylamino)ethyl methacrylate (DMAEMA). The grafting of DMAEMA was characterized by XPS and FT-IR spectroscopic measurements. The adsorption behaviour of DMAEMA-grafted ePTFE (ePTFE-g-PDMAEMA) films was investigated as a function of the experimental parameters, such as the initial pH value, temperature, and grafted amount. The adsorption capacity and initial adsorption rate had the maximum values at the initial pH value of 3.0. On the other hand, the adsorption capacity became almost constant at temperatures higher than 30°C, although the adsorption rate increased over the temperature. The adsorption behaviour obeyed the pseudo-second-order kinetic model and well expressed by the Langmuir isotherm equation with higher correlation coefficients. These results indicate that the adsorption of Cr(VI) ions occurs through the electrostatic interaction between protonated dimethylamino groups on a grafted PDMAEMA chain and HCrO4- ions. Cr(VI) ions were successfully desorbed from Cr(VI)-loaded ePTFE-g-PDMAEMA films in the eluents, such as NaCl at 0.50 M, NH₄Cl at 0.50M, and NaOH at 1.0 mM, and ePTFE-g-PDMAEMA films were repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. It should be noted that Cr(VI) ion adsorptivity with a high initial rate was conferred to the ePTFE films. The results obtained in this study emphasize that ePTFE-g-PDMAEMA films can be applied as an adsorbent for Cr(VI) ions.

Promoted adsorptive removal of chromium(vi) ions from water by a green-synthesized hybrid magnetic nanocomposite (NFe3O4Starch-Glu-NFe3O4ED)

A novel magnetic starch-crosslinked-magnetic ethylenediamine nanocomposite, NFe3O4Starch-Glu-NFe3O4ED, was synthesized via microwave irradiation. The characteristics of the assembled NFe3O4Starch-Glu-NFe3O4ED nanocomposite were evaluated via XRD, FT-IR, TGA, BET, SEM and HR-TEM analyses. Its particle size was confirmed to be in the range 11.25-17.16 nm. The effectiveness of the designed nanocomposite for the removal of Cr(vi) ions was explored using the batch adsorption technique. Equilibrium results proved that the adsorptive removal of the target metal ions from aqueous solution was highly dependent on the optimized experimental parameters. The maximum adsorptive removal percentage values (%R) of Cr(vi) ions on NFe3O4Starch-Glu-NFe3O4ED obtained at pH 2.0 were 85.27%, 91.90%, and 96.47% using 10.0, 25.0, and 50.0 mg L-1 Cr(vi), respectively, for an equilibrium time of 30 min. The adsorption process was found to be strongly influenced by the presence of interfering salts including NaCl, CaCl2, KCl, MgCl2, and NH4Cl. Kinetic studies were performed and it was found that the pseudo-second and Elovich models well fitted the experimental data with the possible suggested ion-pair interaction mechanism. Different isotherm models were employed to assess the adsorption equilibrium, which was revealed by fitting Langmuir, Temkin and Freundlich models. The maximum uptake capacity based on the Langmuir model was 210.741 mg g-1. The effect of temperature and thermodynamics confirmed that adsorption was spontaneous, feasible, and endothermic in nature. Finally, the validity and applicability of using the NFe3O4Starch-Glu-NFe3O4ED nanocomposite to remove Cr(vi) ions from real water matrices were confirmed in the range of 91.2-94.7 ± 2.2-3.7%.

Adsorption-photocatalysis performance of polyaniline/dicarboxyl acid cellulose@graphene oxide for dye removal

A novel 3-D biopolymer-based adsorption-photocatalytic composite, polyaniline/dicarboxyl acid cellulose@graphene oxide was synthesized and was employed to remove the reactive brilliant red K-2G from aqueous solution. The addition of dicarboxyl acid cellulose could improve the morphology, structure, stability and dispersity of the nanocomposite, thus providing excellent adsorption and photocatalysis performance to the product. Batch of experiments were conducted in two scenarios: adsorption followed by photocatalysis process and simultaneous adsorption-photocatalysis process. For the first scenario, adsorption equilibrium can be reached within 25 min, the expected adsorption capacity was 447.0 mg·g^-1; the subsequent photocatalysis process was carried out under light irradiation and the removal capacity could further improve to 729.0 mg·g^-1 under equilibrium state (about 180 min). For the simultaneous adsorption-photocatalytic process, the removal capacity was about 558.1 mg·g^-1 at about 25 min and the total removal capacity could reach to 733.3 mg·g^-1 under equilibrium state. PANI-DCC@GO exhibited excellent reusability and had potential in the treatment of dyes polluted wastewater.

Recent advances in microfluidic-aided chitosan-based multifunctional materials for biomedical applications

Chitosan-based biomaterials has shown great advantages in a broad range of applications, including drug delivery, clinical diagnosis, cell culture and tissue engineering. However, due to the lack of control over the fabrication processes by conventional techniques, the wide application of chitosan-based biomaterials has been hampered. Recently, microfluidics has been demonstrated as one of the most promising platforms to fabricate high-performance chitosan-based multifunctional materials with monodisperse size distribution and accurately controlled morphology and microstructures, which show great promising for biomedical applications. Here, we review recent progress of the fabrication of chitosan-based biomaterials with different structures and integrated functions by microfluidic technology. A comprehensive and in-depth depiction of critical microfluidic formation mechanism and process of various chitosan-based materials are first interpreted, with particular descriptions about the microfluidic-mediated control over the morphology and microstructures. Afterwards, recently emerging representative applications of chitosan-based multifunctional materials in various fields, are systematically summarized. Finally, the conclusions and perspectives on further advancing the microfluidic-aided chitosan-based multifunctional materials toward potential and versatile development for fundamental researches and biomedicine are proposed.

Synthesis of sodium lignosulfonate-guar gum composite hydrogel for the removal of Cu2+ and Co2

As an emerging pollutant treatment material, hydrogel is known for its good adsorption capacity and environmental friendliness. In this study, a composite material of acrylic acid as the polymerization monomer grafted sodium lignosulfonate and guar gum was prepared, which provided a channel for adsorbing metal ions with its abundant active functional groups and porous structure. The optimized synthesized product was applied to the removal of Cu²⁺ and Co²⁺ in a one-component system and a multi-component system, and the maximum ion adsorption capacities obtained were determined to be 709 mg g^-1 of Cu²⁺, 601 mg g^-1 of Co²⁺, respectively. The adsorption kinetics and isotherms were well fitted by the pseudo second-order kinetic model and the Langmuir isotherm, showing that the adsorption of Cu²⁺ and Co²⁺ by the adsorbent belongs to the chemisorption on monolayer. XPS results confirmed the successful adsorption of Cu²⁺ and Co²⁺ by GG/SLS. Surface complexation was proposed to be the main mechanism for GG/SLS adsorbent to remove heavy metal ions. In addition, the use of recycling research showed that the adsorbent has good chemical stability. These results provided valuable information for designing highly efficient adsorbents that can be used as a high-quality wastewater treatment material.

Efficient Removal Of U(VI) Ions from Aqueous Solutions by Tannic Acid/Graphene Oxide Composites

Tannic acid/graphene oxide (TA/GO) composites were prepared in the present research, and their properties and sorption performance were evaluated by corresponding characterization methods and bath sorption experiments, respectively. The applications of TA/GO to remove U(VI) from aqueous solution were investigated with the maximum adsorption capacity of 87.8 mg·g−1 at low pH (pH = 3.6 ± 0.03). The sorption of U(VI) ions on TA/GO followed the Langmuir model because of the complexation of oxygen-containing functional groups on the surface of TA/GO composites and uranium ions. TA/GO manifested excellent selective adsorption toward uranium ions with other metal ions (Cs+, Sr2+, Co2+). Furthermore, TA/GO as an effective adsorbent was reused to remove a large amount of U(VI) ions from aqueous solution. Therefore, TA/GO is an ideal material to remove highly toxic U(VI) ions from wastewater.

Statistical optimization of textile dye effluent adsorption by Gracilaria edulis using Plackett-Burman design and response surface methodology

Statistical optimization models were employed to optimize the adsorption of textile dye effluent onto Gracilaria edulis. Significant factors responsible for adsorption were determined using Plackett-Burman design (PBD) and were time, pH, and dye concentration. Box-Behnken (BB) design was used for further optimization. The predicted and the experimental values were found to be in good agreement, the coefficient of determination value 0.9935 and adjusted coefficient of determination value 0.9818 indicated that the model was significant. The results of predicted response optimization showed that maximum decolorization could be attained with time 131.51 min, pH 7.48, and dye concentration 23.13%. The model was validated experimentally with 92.65% decolorization efficiency. The experiment was confirmed using Fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscope coupled with energy dispersive X-ray analysis (HR-SEM-EDX), X-ray diffraction spectrometry (XRD) and Brunauer-Emmett-Teller (BET) surface area and pore size analysis techniques. Desorption studies at various pH (2–14) were performed and a maximum of 23% of the dye was recovered from the adsorbed biomass.