The one-step synthesis of a novel metal-organic frameworks for efficient and selective removal of Cr(VI) and Pb(II) from wastewater: Kinetics, thermodynamics and adsorption mechanisms

Multifunctional natural starch-based hydrogels: Critical characteristics, formation mechanisms, various applications, future perspectives

With the growth of the global population and increasing concern for environmental issues, the development of sustainable and eco-friendly materials has become increasingly important. Starch, as a renewable resource, is one of the most abundant polysaccharides in nature, with the advantages of good biocompatibility, high biodegradability, and low cost. Starch-based hydrogels (SBHs) have attracted widespread attention due to their unique physical and chemical properties. This article provides a comprehensive review of the latest research progress in SBHs, discussing their main characteristics, formation mechanisms, diverse applications, and future development trends. First, it outlines the biocompatibility, degradability, water absorption and retention, environmental responsiveness, and mechanical strength of SBHs. Then, it elaborates in detail on the formation mechanisms of SBHs, including physical crosslinking (hydrogen bonding, electrostatic interactions, host-guest and coordination interactions), chemical crosslinking (such as initiators, heat, light, radiation, and click reactions), and synergistic effects. Subsequently, it analyzes the applications of SBHs in cutting-edge fields such as flexible sensors, medical dressings, drug delivery, tissue engineering, soil protection, wastewater treatment, and food packaging. Finally, it summarizes the challenges in current research and provides an outlook on future development trends, emphasizing the importance of further optimizing the performance of SBHs to meet broader industrial needs and environmental protection goals. This review not only provides a systematic theoretical framework for the study of SBHs but also charts a course for their innovative applications in the field of sustainable materials, playing a significant role in advancing the continuous development of this area.

Exploring the state-of-the-art in metal-organic frameworks for antibiotic adsorption: a review of performance, mechanisms, and regeneration

The application of metal-organic frameworks (MOFs) towards the adsorption of antibiotics is a new and emerging area of study. The rise in use or misuse of antibiotic products has exacerbated their ongoing presence and persistence in the natural environment. Even at low concentrations, antibiotic residues exert pressure on bacterial populations, eventually leading to the emergence of resistant bacteria. Metal-organic frameworks, known for their high porosity, vast specific surface area, and ease of modification, have emerged to be a promising and sustainable antibiotic adsorbent. In an effort to advance the development of this adsorbent, this study provides a state-of-the-art review of recent research published from 2020 to the present, specifically examining the use of MOFs for removing antibiotics from aqueous solutions. Multiple MOF adsorbents were analyzed, with approximately 59% demonstrating significant adsorption capacity within the pH range of 6.0-8.0. In 75% of the instances, the adsorption system reached equilibrium in under 2 hr. Adsorption capacities compared well to other published works in the literature and exceeded conventional adsorbents in many instances. Notable cases of MOF performance were MIL-53(Al) adsorption of amoxicillin (AMX) and SA-g-P3AP@MOF(Fe)/Ag adsorption of neomycin where adsorption capacities of 758.5 and 625.0 mg/g were attained, respectively. The reusability of MOFs was extensively reported at the laboratory batch scale. Analysis of the reported studies revealed the most effective eluents were acetone, ethanol, and methanol, with mostly 3-5 cycles attainable without appreciable loss in efficiency. The recent literature confirmed that MOFs are highly efficient in the adsorption of antibiotics; however, there are some areas that warrant further development. It is intended that this work will bring recent trends to the forefront, identify knowledge gaps, and help guide future research proposals.

Greener Synthesis of Poly(LIM-co-DVB-co-AMPS): A Sustainable Approach to Methylene Blue Removal

A novel environmentally friendly adsorbent, poly(limonene-co-divinylbenzene-co-2-acrylamido-2-methyl-1-propanesulfonic acid, LIM-co-DVB-co-AMPS), was synthesized and applied for the adsorption of methylene blue from aqueous solutions in this study. The structure, morphology, and thermal stability of the green adsorbent were determined by the FTIR, SEM, TGA/DTA/DTG, and BET techniques, ζ potential, and elemental analysis. The efficiency of the adsorption process was improved with respect to several experimental conditions, viz., adsorbent dose, pH, and contact time. The adsorption process was found to fit very well with the Langmuir isotherm and the pseudo-second-order model. Benefiting from the higher number of surface sites, porous structure, and good surface area, poly(LIM-co-DVB-co-AMPS) particles exhibited a superior adsorption performance for MB with a Langmuir adsorption capacity of 98 mg g-1. The selectivity of the sorbent does not depend on the coexisting ions, and the sorbent is applicable in complex matrixes in the presence of these ions. The elution process was employed using ethanol within a 1.0 M hydrochloric acid (HCl) medium, leading to a remarkable usability exceeding 90% even after five consecutive adsorption/desorption cycles. Spike recovery experiments conducted using real water samples substantiate the practical applicability of the adsorbent. The high efficiency, utilization of cost-effective materials, and ease of fabrication, coupled with their selective nature and lower environmental impact through sorbent reuse, collectively confer superior advantages. These distinctive features render the environmentally benign adsorbent highly applicable for promising applications in the removal of methylene blue from aqueous solutions.

Novel chitosan/lignin hydrogel prepared by the Mannich reaction for Pb(II) and Cu(II) removal from aqueous solution

Green and high-performance biomass-based adsorbents have a good application prospect for the removal of heavy metals. At present, the preparation of chitosan/lignin biomass adsorbents mainly adopts dissolution-drying method, and the obtained adsorbents show relatively poor adsorption performance for heavy metals. To overcome this problem, a novel chitosan/lignin hydrogel (CSL) is prepared by a simple one-pot method through the Mannich reaction. Research findings show that the hydrogels present higher adsorption selectivity for Pb(II) and Cu(II) than other common heavy metals. Among them, the optimal hydrogel CSL1 shows unexpectedly ultrafast adsorption rate for Pb(II) and Cu(II) with equilibrium time of only 1 min and 2 min. Meanwhile, the maximum adsorption capacities of CSL1 for Pb(II) and Cu(II) are 139.86 and 98.71 mg·g-1, respectively. Compared with the reported adsorption materials related to chitosan or lignin, the CSL1 has the advantages of simple preparation process, considerable adsorption capacity, and short adsorption equilibrium time. Moreover, the adsorption mechanism is investigated by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the results prove that the adsorption mechanism is chemical complexation. This work not only contributes to the advancement of hydrogel-based adsorbents, but also holds significant industrial potential for addressing water pollution issues and promoting sustainable development.

Uptake of lead, cadmium and copper by heavy metal-resistant Pseudomonas aeruginosa strain DR7 isolated from soil

This study highlights the biosorption capacity for Cd (II), Cu (II) and Pb (II) by a locally isolated Pseudomonas aeruginosa DR7. At initial concentrations of 150 mg L-1 and 240 min of contact time, P. aeruginosa DR7 showed a 62.56 mg/g removal capacity for Cd (II) at an optimum pH of 6.0, 72.49 mg/g for Cu (II) at an optimum pH of 6.0, and 94.2 mg/g for Pb (II) at an optimum pH of 7.0. The experimental data of Cd (II), Cu (II), and Pb (II) adsorbed by the pseudo-second-order kinetic model correlates well with P. aeruginosa DR7, with R2 all above 0.99, showing that the fitting effect was satisfactory. The isothermal adsorption processes of Cd (II) (0.980) and Cu (II) (0.986) were more consistent with the Freundlich model, whereas Pb (II) was more consistent with the Langmuir model (0.978). FTIR analysis suggested the involvement of hydroxyl, carbonyl, carboxyl, and amine groups present in the inner regions of P. aeruginosa cells during the biosorption process. SEM-EDS analysis revealed that after contact with metals, there were slight changes in the surface appearance of the cells, which confirmed the deposition of metals on the bacterial surface. There was also the possibility of the metals being translocated into the bacterial inner regions by the appearance of electron-dense particles, as observed using TEM. As a conclusion, the removal of metals from solutions using P. aeruginosa DR7 was a plausible alternative as a safe, cheap, and easily used biosorbent.

Controllable fabrication of SbxBi2-xS3 solid solution photocatalysts with superior elimination for Cr(VI)

The development of environmentally friendly and cost-effective photocatalysts is of vital significance for the effective removal of heavy metal contamination in water, but it is still a crucial challenge. Herein, the novel SbxBi2-xS3 solid solution photocatalysts with a certain amount of sulfur vacancy were prepared by adjusting the molar ratio of Sb to Bi through a simple hydrothermal strategy, and was applied to the effective photocatalytic reduction of hexavalent chromium (Cr(VI)). Sb1.75Bi0.25S3 with optimized ratio has superior reduction performance of Cr(VI), and the photocatalytic efficiency of Cr(VI) can achieve 91.9 % within 1 h of visible light illumination. The remarkable catalytic efficiency is due to the more applicable band structure of the solid solution photocatalyst, which is conducive for the photocatalytic reaction. Moreover, the substitution of Bi causes the crystal distortion of Sb2S3 and induce the generation of sulfur defects, which can effectively capture photoelectrons, accelerate the carriers separation, and improve the reduction performance. This study provides a hopeful photocatalyst for wastewater purification and promotes the exploration of solid solution photocatalyst in water environment remediation.

Sustainable Biomass Acts as an Electron Donor for Cr(VI) Reduction during the Subcritical Hydrothermal Process: Molecular Insights into the Role of Hydrochar and Liquid Compounds

Heavy metal pollution is a critical environmental issue that has garnered significant attention from the international community. Subcritical hydrothermal liquefaction (HTL) as an emerging green technology has demonstrated remarkable promise in environmental remediation. However, there is limited research on the remediation of highly toxic Cr(VI) using HTL. This study reveals that the HTL reaction of biomass enables the simultaneous reduction and precipitation of Cr(VI). At 280 °C, the reduction of Cr(VI) was nearly complete, with a high reduction rate of 98.9%. The reduced Cr as Cr(OH)3 and Cr2O3 was primarily enriched in hydrochar, accounting for over 99.9% of the total amount. This effective enrichment resulted in the removal of Cr(VI) from the aqueous phase while simultaneously yielding clean liquid compounds like organic acids and furfural. Furthermore, the elevated temperature facilitated the formation of Cr(III) and enhanced its accumulation within hydrochar. Notably, the resulting hydrochar and small oxygenated compounds, especially aldehyde, served as electron donors for Cr(VI) reduction. Additionally, the dissolved Cr facilitated the depolymerization and deoxygenation processes of macromolecular compounds with lignin-like structures, leading to more small oxygenated compounds and subsequently influencing Cr(VI) reduction. These findings have substantial implications for green and sustainable development.

Enhanced Cr(VI) removal via CPBr-modified MIL-88A@amine-functionalized GO: synthesis, performance, and mechanism

Water contamination by heavy metals, especially chromium (VI), poses a critical environmental issue due to its carcinogenic nature and persistence in the environment. Addressing this, the current study develops an efficient adsorbent, CPBr-MIL-88A@AmGO, which utilizes the synergistic capabilities of Cetylpyridinium bromide-modified MIL-88A and amine-functionalized graphene oxide to enhance Cr(VI) removal from aqueous solutions. The obtained results indicate that CPBr-MIL-88A@AmGO achieves its highest removal efficacy at pH 2, where the interaction of CPBr and AmGO's positively charged centers significantly contributes to the adsorption processes. According to the Langmuir isotherm model, the composite's adsorption capacity reached a maximum of 306.75 mg/g. The adsorption kinetics adhered to a pseudo-second-order model along with the endothermic nature of the process. Although the presence of SO42- ions significantly reduces adsorption capacity, other interfering ions including Na+, K+, Ca2+, Cl-, and NO3- only slightly affect it. Remarkably, the composite maintains high removal efficiency, over 82%, even after 7 recycling tests, underscoring its potential for practical applications in water treatment systems. The proposed mechanism involves the contribution of electrostatic attractions, ion exchange, complexation, and the reduction of Cr(VI) to Cr(III) in the removal process. This study not only offers a potent solution for Cr(VI) remediation but also contributes to sustainable water resource management.

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.

Heavy metal sequestration from wastewater by metal-organic frameworks: a state-of-the-art review of recent progress

Metal-organic frameworks (MOFs) have emerged as highly promising adsorbents for removing heavy metals from wastewater due to their tunable structures, high surface areas, and exceptional adsorption capacities. This review meticulously examines and summarizes recent advancements in producing and utilizing MOF-based adsorbents for sequestering heavy metal ions from water. It begins by outlining and contrasting commonly employed methods for synthesizing MOFs, such as solvothermal, microwave, electrochemical, ultrasonic, and mechanochemical. Rather than delving into the specifics of adsorption process parameters, the focus shifts to analyzing the adsorption capabilities and underlying mechanisms against critical metal(loid) ions like chromium, arsenic, lead, cadmium, and mercury under various environmental conditions. Additionally, this article discusses strategies to optimize MOF performance, scale-up production, and address environmental implications. The comprehensive review aims to enhance the understanding of MOF-based adsorption for heavy metal remediation and stimulate further research in this critical field. In brief, this review article presents a comprehensive overview of the contemporary information on MOFs as an effective adsorbent and the challenges being faced by these adsorbents for heavy metal mitigation (including stability, cost, environmental issues, and optimization), targeting to develop a vital reference for future MOF research.

Determination of parabens in breast milk using stir bar sorptive extraction coupled with UHPLC-UV

We developed an analytical method based on ultra-high performance liquid chromatography with UV detection, using a stir bar coated with amino/hydroxyl bifunctional microporous organic network (B-MON), for the analysis of parabens in breast milk samples. B-MON demonstrated superior performance with maximal methylparaben adsorption of 112.15 mg/g. Kinetic fitting revealed that outer diffusion was the key limiting step, and the adsorption was chemisorption. The thermodynamic analysis demonstrated that increased methylparaben adsorption was found at higher temperatures in spontaneous processes. The developed approach showed excellent linearity (R2 ≥ 0.9964) and a low detection limit (0.01 μg/L). Recoveries ranged from 85.8 to 105.5 % and the relative standard deviation was lower than 9.2 %. Based on the daily exposure assessment, these pollutants do not pose unacceptable health hazards to babies. However, the high detection frequencies (41.9%-93.5 %) suggest that breast milk still should be monitored.

Selective adsorption of Cr(VI) by nitrogen-doped hydrothermal carbon in binary system

Selective adsorption of heavy metal ions from industrial effluent is important for healthy ecosystem development. However, the selective adsorption of heavy metal pollutants by biochar using lignin as raw material is still a challenge. In this paper, the lignin carbon material (N-BLC) was synthesized by a one-step hydrothermal carbonization method using paper black liquor (BL) as raw material and triethylene diamine (TEDA) as nitrogen source. N-BLC (2:1) showed excellent selectivity for Cr(VI) in the binary system, and the adsorption amounts of Cr(VI) in the binary system were all greater than 150 mg/g, but the adsorption amounts of Ca(II), Mg(II), and Zn(II) were only 19.3, 25.5, and 6.3 mg/g, respectively. The separation factor (SF) for Cr(VI) adsorption was as high as 120.0. Meanwhile, FTIR, elemental analysis and XPS proved that the surface of N-BLC (2:1) contained many N- and O- containing groups which were favorable for the removal of Cr(VI). The adsorption of N-BLC (2:1) followed the Langmuir model and its maximum theoretical adsorption amount was 618.4 mg/g. After 5th recycling, the adsorption amount of Cr(VI) by N-BLC (2:1) decreased about 15%, showing a good regeneration ability. Therefore, N-BLC (2:1) is a highly efficient, selective and reusable Cr(VI) adsorbent with wide application prospects.

Orientation Growth of N-Doped and Iron-Based Metal-Organic Framework and Its Application for Removal of Cr(VI) in Wastewater

A series of NH2-functionalized nano-sized magnetic metal-organic frameworks (MOFs) were prepared in this study for Cr(VI) removal from wastewater. It was observed that not only the morphological, i.e., orientation growth of N-doped and iron-based metal-organic frameworks, but also the adsorption of magnetic MOFs is largely related to the used amount of ammonium hydroxide in preparation. For example, with increasing amounts of ammonium hydroxide used in preparation, the morphology of magnetic MOFs changed from spherical to cube and triangular cone. Moreover, the maximum adsorption capacity of spherical-magnetic MOFs, cubic-magnetic MOFs and triangular cone-magnetic MOFs could be up to 204.08 mg/g, 232.56 mg/g and 270.27 mg/g, respectively. Under optimal conditions, the adsorption process of magnetic MOFs for Cr(VI) was consistent with the pseudo-second-order rate equation (R2 = 1) and Langmuir isotherm model (R2 > 0.99). Therefore, magnetic MOFs developed in this work offered a viable option for the removal of Cr(VI) from wastewater.

Fluorescent starch-based hydrogel with cellulose nanofibrils and carbon dots for simultaneous adsorption and detection of Pb(II)

The adsorption removal of lead (Pb) ions has become a crucial area of research due to the potential health hazards associated with Pb contamination. Developing cost-effective adsorbents for the removal of Pb(II) ions is significantly important. Hence, a novel fluorescent starch-based hydrogel (FSH) using starch (ST), cellulose nanofibrils (CN), and carbon dots (CD) was fabricated for simultaneous adsorption and detection of Pb(II). A comprehensive characterization of FSH, including its morphological features, chemical composition, and fluorescence characteristics, was conducted. Notably, FSH exhibited a maximum theoretical adsorption capacity of 265.9 mg/g, which was 13.0 times higher than that of pure ST. Moreover, FSH was employed as a fluorescent sensor for Pb(II) determination, achieving a limit of detection (LOD) of 0.06 μg/L. An analysis was further performed to investigate the adsorption and detection mechanisms of Pb(II) utilizing FSH. This study provides valuable insights into the production of a novel cost-effective ST-based adsorbent for the removal of Pb(II) ions.

Nitric Acid-Treated Blue Coke-Based Activated Carbon's Structural Characteristics and Its Application in Hexavalent Chromium-Containing Wastewater Treatment

This study primarily focused on the efficient transformation of low-priced blue coke powder into a high-capacity adsorbent and aimed to address the pollution issue of hexavalent chromium (Cr (VI))-laden wastewater and to facilitate the effective utilization of blue coke powder. A two-step method was utilized to fabricate a blue coke-based nitric acid-modified material (LCN), and the impact of nitric acid modification on the material's structure and its efficacy in treating Cr (VI)-contaminated wastewater was evaluated. Our experimental results illustrated that, under identical conditions, LCN exhibited superior performance for Cr (VI) treatment compared to the method employing only potassium hydroxide (LCK). The specific surface area and pore volume of LCN were 1.39 and 1.36 times greater than those of LCK, respectively. Further chemical composition analysis revealed that the functional group structure on the LCN surface was more conducive to Cr (VI) adsorption. The highest amount of Cr (VI) that LCN could bind was measured at 181.962 mg/g at 318 K. This was mostly due to chemisorption, which is dominated by redox reactions. The Cr (VI) removal process by LCN was identified to be a spontaneous, exothermic, and entropy-increasing process. Several tests on recycling and reuse showed that LCN is a stable and effective chromium-containing wastewater adsorbent, showing that it could be used in many situations.

Preparation and characterization of Allium cepa extract coated biochar and adsorption performance for hexavalent chromium

The elimination of hazardous metal ions from contaminated water has been an important procedure to improve the quality of the water source. Hence, this study presents the fabrication of Allium cepa extract-coated biochar for the elimination of Cr (VI) from wastewater. The synthesized biochar (SBCH) and modified biochar (BMOJ) were characterized by making use of FTIR, BET, XRD, TGA and SEM. Optimum Cr (VI) removal was achieved at solution pH 2, 0.05 g adsorbent dosage and 180 min agitation period. The adsorptive removal of Cr (VI) onto SBCH and BMOJ followed the pseudo-second-order kinetic model with a satisfactory sum of square residuals (SSR) of 3.874 and 5.245 for SBCH and BMOJ, respectively. Meanwhile, Freundlich isotherm was found to best describe the uptake of Cr (VI) SBCH and BMOJ. Experimental data showed an adsorption capacity of 37.38 and 25.77 mg g-1 and a maximum efficiency of 85.42% and 51.63% for BMOJ and SBCH, respectively. BMOJ also showed good antioxidant characteristics. Thermodynamic data revealed that the uptake of Cr (VI) onto the SBCH and BMOJ was an exothermic and endothermic (ΔH: SBCH =  - 16.22 kJ mol-1 and BMOJ = 13.74 kJ mol-1), entropy-driven (ΔS: SBCH = 40.96 J K-1 mol-1 and BMOJ = 93.26 J K-1 mol-1) and spontaneous process. Furthermore, BMOJ demonstrated excellent reusability and promising characteristics for industrial applications.

A novel CNTs/QCS/BiOBr composite membrane with electron-ion transfer channel for Br- recovery in ESIX process

Based on the superior selectivity of bismuth oxybromide (BiOBr) for Br^-, the excellent electrical conductivity of carbon nanotubes (CNTs), and the ion exchange capacity of quaternized chitosan (QCS), a three-dimensional network composite membrane electrode CNTs/QCS/BiOBr was constructed, in which BiOBr served as the storage space for Br^-, CNTs provided the electron transfer pathway, and QCS cross-linked by glutaraldehyde (GA) was used for ion transfer. The CNTs/QCS/BiOBr composite membrane exhibits superior conductivity after the introduction of the polymer electrolyte, which is seven orders of magnitude higher than that of conventional ion-exchange membranes. Furthermore, the addition of the electroactive material BiOBr improved the adsorption capacity for Br^- by a factor of 2.7 in electrochemically switched ion exchange (ESIX) system. Meanwhile, the CNTs/QCS/BiOBr composite membrane displays excellent Br^- selectivity in mixed solutions of Br^-, Cl^-, SO₄^2- and NO₃^-. Therein, the covalent bond cross-linking within the CNTs/QCS/BiOBr composite membrane endows it great electrochemical stability. The synergistic adsorption mechanism of the CNTs/QCS/BiOBr composite membrane provides a new direction for achieving more efficient ion separation.