Mesoporous Biopolymer Architecture Enhanced the Adsorption and Selectivity of Aqueous Heavy-Metal Ions

Cefixime loaded bare and functionalized halloysite nanocarriers and their biomedical applications

Effective drug delivery for is the foremost requirement for the complete recovery of the disease. Nanomedicine and nanoengineering has provided so many spaces and ideas for the drug delivery design, whether controlled, targeted, or sustained. Different types of nanocarriers or nanoparticles are aggressively designed for the drug delivery applications. Clay minerals are identified as a one of the potential nanocarrier for the drug delivery. Owing to their biocompatibility and very low cytotoxicity, clay minerals showing effective therapeutic applications. In the present investigation, clay mineral, i.e., Halloysite nano tubes are utilized as a nanocarrier for the delivery of antibiotic cefixime (CFX), a third-generation cephalosporin. The HNT was first functionalized with the sulfuric acid and then further treated with the 3-(aminopropyl)triethoxysilane (APTES). The drug is loaded on three different classifications of HNTs, i.e., Bare-CFX-HNT, Acid-CFX-HNT, and APTES-CFX-HNT and their comparative analysis is established. Different characterization techniques such as X-ray diffractometry (XRD), Fourier transform infra-red (FT-IR), Transmission electron microscopy TEM), Brunauer-Emmett-Teller (BET), adsorption studies, and Thermogravimetric analysis (TGA) were performed to evaluate their chemical, structural, morphological, and thermal properties. TGA confirmed the encapsulation efficiency of Bare-CFX-HNT, Acid-CFX-HNT, and APTES-CFX-HNT as 42.65, 52.19, and 53.43%, respectively. Disk diffusion and MTT assay confirmed that the drug loaded HNTs have potential antibacterial activities and less cytotoxicity. The adsorption capacity of CFX with different HNTs are evaluated and Different adsorption and kinetic models have been discussed. Drug release studies shows that APTES-CFX-HNT showing sustained release of cefixime as compared to Bare-CFX-HNT and Acid-CFX-HNT.

Rapidly reducing cadmium from contaminated farmland soil by novel magnetic recyclable Fe3O4/mercapto-functionalized attapulgite beads

Reducing cadmium (Cd) content from contaminated farmland soils remains a major challenge due to the difficulty in separating commonly used adsorbents from soils. This study synthesized novel millimeter-sized magnetic Fe3O4/mercapto-functionalized attapulgite beads (MFBs) through a facile one-step gelation process incorporating alginate. The MFBs inherit the environmental stability of alginate and enhance its mechanical strength by hybridizing Fe3O4 and clay mineral components. MFBs can be easily separated from flooded soils by magnets. When applied to 12 Cd-polluted paddy soils and 14 Cd-polluted upland soils, MFBs achieved Cd(II) removal rates ranging from 16.9% to 62.2% and 9.8%-54.6%, respectively, within a 12-h period. The MFBs predominantly targeted the exchangeable and acid soluble, and reducible fractions of Cd, with significantly enhanced removal efficiencies in paddy soils compared to upland soils. Notably, MFBs exhibited superior adsorption performance in soils with lower pH and organic matter (OM) content, where the bioavailability and mobility of Cd are heightened. The reduction of Cd content by MFBs is a sustainable and safe method, as it permanently removes the bioavailable Cd from soil, rather than temporarily reducing its bioavailability. The functional groups such as -SH, -OH, present in attapulgite and alginate of MFBs, played a crucial role in Cd(II) adsorption. Additionally, attapulgite and zeolite provided a porous matrix structure that further enhanced Cd(II) adsorption. The results of X-ray photoelectron spectroscopy suggested that both chemical precipitation and surface complexation contributed to Cd(II) removal. The MFBs maintained 87.6% Cd removal efficiency after 5 regeneration cycles. The surface of the MFBs exposed new adsorption sites and increased the specific surface area during multiple cycles with Cd-contaminated soil. This suggests that MFBs treatment with magnetic retrieval is a potentially effective pathway for the rapid removal of Cd from contaminated farmland soils.

Almond shell-derived biochar decreased toxic metals bioavailability and uptake by tomato and enhanced the antioxidant system and microbial community

The effectiveness of almond shell-derived biochar (ASB) in immobilizing soil heavy metals (HMs) and its impact on soil microbial activity and diversity have not been sufficiently studied. Hence, a pot study was carried out to investigate the effectiveness of ASB addition at 2, 4, and 6 % (w/w) on soil biochemical characteristics and the bioavailability of Cd, Cu, Pb, and Zn to tomato (Solanum lycopersicum L.) plants, as compared to the control (contaminated soil without ASB addition). The addition of ASB promoted plant growth (up to two-fold) and restored the damage to the ultrastructure of chloroplast organelles. In addition, ASB mitigated the adverse effects of HMs toxicity by decreasing oxidative damage, regulating the antioxidant system, improving soil physicochemical properties, and enhancing enzymatic activities. At the phylum level, ASB addition enhanced the relative abundance of Actinobacteriota, Acidobacteriota, and Firmicutes while decreasing the relative abundance of Proteobacteria and Bacteroidota. Furthermore, ASB application increased the relative abundance of several fungal taxa (Ascomycota and Mortierellomycota) while reducing the relative abundance of Basidiomycota in the soil. The ASB-induced improvement in soil properties, microbial community, and diversity led to a significant decrease in the DTPA-extractable HMs down to 41.0 %, 51.0 %, 52.0 %, and 35.0 % for Cd, Cu, Pb, and Zn, respectively, as compared to the control. The highest doses of ASB (ASB6) significantly reduced the metals content by 26.0 % for Cd, 78.0 % for Cu, 38.0 % for Pb, and 20.0 % for Zn in the roots, and 72.0 % for Cd, 67.0 % for Cu, 46.0 % for Pb, and 35.0 % for Zn in the shoots, as compared to the control. The structural equation model predicts that soil pH and organic matter are driving factors in reducing the availability and uptake of HMs. ASB could be used as a sustainable trial for remediation of HMs polluted soils and reducing metal content in edible plants.

Cellulose-Based Hydrogels for Wastewater Treatment: A Focus on Metal Ions Removal

The rapid worldwide industrial growth in recent years has made water contamination by heavy metals a problem that requires an immediate solution. Several strategies have been proposed for the decontamination of wastewater in terms of heavy metal ions. Among these, methods utilizing adsorbent materials are preferred due to their cost-effectiveness, simplicity, effectiveness, and scalability for treating large volumes of contaminated water. In this context, heavy metal removal by hydrogels based on naturally occurring polymers is an attractive approach for industrial wastewater remediation as they offer significant advantages, such as an optimal safety profile, good biodegradability, and simple and low-cost procedures for their preparation. Hydrogels have the ability to absorb significant volumes of water, allowing for the effective removal of the dissolved pollutants. Furthermore, they can undergo surface chemical modifications which can further improve their ability to retain different environmental pollutants. This review aims to summarize recent advances in the application of hydrogels in the treatment of heavy metal-contaminated wastewater, particularly focusing on hydrogels based on cellulose and cellulose derivatives. The reported studies highlight how the adsorption properties of these materials can be widely modified, with a wide range of adsorption capacity for different heavy metal ions varying between 2.3 and 2240 mg/g. The possibility of developing new hydrogels with improved sorption performances is also discussed in the review, with the aim of improving their effective application in real scenarios, indicating future directions in the field.

Construction of hyperbranched imprinted nanomaterials for selective adsorption of cadmium (II)

A hyperbranched ion-imprinted polymer (IIP) material containing multiple selective adsorption sites was synthesized using halloysite nanotubes, methyl acrylate, and ethylenediamine in the presence of a template ion [i.e. Cd (II) heavy metal]. The successful preparation of the Cd-IIP composition was confirmed by FT-IR, XRD, TEM, TGA, and elemental analysis. The polymers exhibited good adsorption of Cd (II) with a maximum adsorption capacity of 64.37 mg·g-1. The imprinting factor (α) for Cd (II) was 2.62 and the selection factor (β) was 1.78, indicating a specific adsorption of Cd (II) ion. The selection coefficients of Cd-IIP for Cd (II)/Pb (II), Cd (II)/Cu (II), Cd (II)/Ni (II), Cd (II)/Cr (III), and Cd (II)/Na (I) also indicated an excellent selectivity of the hyperbranched polymers for Cd (II) in the presence of competitive ions. The removal efficiency remained more than 75% after five cycles of desorption/adsorption. We envision that the HNTs based Cd-IIP has promising applications in the removal of Cd (II) from wastewater.

Remarkable adsorption of As(V) by Fe3+ and Mg2+ modified alginate porous beads (Fe/Mg-SA) via a facile method

Although sodium alginate (SA) is frequently utilized because of its good gelling properties, the substance's dearth of adsorption active sites prevents it from effectively removing heavy metals. Herein, SA was used as the base material to form a cross-linked structure with Fe3+ and Mg2+, and gel beads with a diameter of 2.0 ± 0.1 mm with specific adsorption on As(V) were synthesized as adsorbent (Fe/Mg-SA). Fe/Mg-SA was systematically characterized, and its adsorption properties were investigated by varying several conditions. Fe/Mg-SA had a wide pH application range. The adsorption kinetics revealed that a quasi-secondary kinetic model was followed. The adsorption process is linked to the complexation of hydroxyl and AsO43-, chemisorption predominated the adsorption process. The maximal adsorption capacity of Fe/Mg-SA is determined by fitting the Langmuir model to be 37.4 mg/g. Compared to other adsorbents, it is simpler to synthesis, more effective and cheaper. Each treatment of 1 m3 wastewater of Fe/Mg-SA only costs ¥ 38.612. The novel gel beads synthesized provides a better option for purifying groundwater contaminated with As(V).

Heavy metal stabilization remediation in polluted soils with stabilizing materials: a review

The remediation of soil contaminated by heavy metals has long been a concern of academics. This is due to the fact that heavy metals discharged into the environment as a result of natural and anthropogenic activities may have detrimental consequences for human health, the ecological environment, the economy, and society. Metal stabilization has received considerable attention and has shown to be a promising soil remediation option among the several techniques for the remediation of heavy metal-contaminated soils. This review discusses various stabilizing materials, including inorganic materials like clay minerals, phosphorus-containing materials, calcium silicon materials, metals, and metal oxides, as well as organic materials like manure, municipal solid waste, and biochar, for the remediation of heavy metal-contaminated soils. Through diverse remediation processes such as adsorption, complexation, precipitation, and redox reactions, these additives efficiently limit the biological effectiveness of heavy metals in soils. It should also be emphasized that the effectiveness of metal stabilization is influenced by soil pH, organic matter content, amendment type and dosage, heavy metal species and contamination level, and plant variety. Furthermore, a comprehensive overview of the methods for evaluating the effectiveness of heavy metal stabilization based on soil physicochemical properties, heavy metal morphology, and bioactivity has also been provided. At the same time, it is critical to assess the stability and timeliness of the heavy metals' long-term remedial effect. Finally, the priority should be on developing novel, efficient, environmentally friendly, and economically feasible stabilizing agents, as well as establishing a systematic assessment method and criteria for analyzing their long-term effects.

Iron-modified biochar derived from sugarcane bagasse for adequate removal of aqueous imidacloprid: sorption mechanism study

Adsorption has been considered as a promising remediation technology to separate organic and inorganic agrochemicals from contaminated soil and water. Low-cost adsorbents, including waste derived materials, clay composites, biochar, and biochar modified materials, have attracted enormous attention for the removal of organic contaminants, including pesticides. In this study, iron-modified base-activated biochar (FeBBC) was prepared by pyrolysis (at 400 °C for 1 h) of iron-doped base (KOH) activated sugarcane bagasse for the removal of a widely used insecticide, namely imidacloprid (IMI) from water. The maximum adsorption capacity of the adsorbent (FeBBC) was calculated as 10.33 (± 1.57) mg/g from Langmuir isotherm model. The adsorbents could remove up to ~ 92% of IMI from aqueous solution at 23.8 mg/L IMI. Experimental data fitted well with the Freundlich model and pseudo-second-order model, demonstrating physisorption, as well as chemosorption, contributed to the sorption process. Even at highly acidic/basic solution pH, the FeBBC could remove substantial amount of IMI demonstrating hydrophobic interaction and pore diffusion play vital role for removal of IMI. The slight improving of IMI sorption with increasing solution pH indicated the sorption was also facilitated through ionic interaction alongside physical sorption. However, physical sorption including hydrophobic interaction and pore-filling interaction plays a vital role in the sorption of IMI.

Sodium Alginate/β-Cyclodextrin Reinforced Carbon Nanotubes Hydrogel as Alternative Adsorbent for Nickel(II) Metal Ion Removal

Water pollution issues, particularly those caused by heavy metal ions, have been significantly growing. This paper combined biopolymers such as sodium alginate (SA) and β-cyclodextrin (β-CD) to improve adsorption performance with the help of calcium ion as the cross-linked agent. Moreover, the addition of carbon nanotubes (CNTs) into the hybrid hydrogel matrix was examined. The adsorption of nickel(II) was thoroughly compared between pristine sodium alginate/β-cyclodextrin (SA-β-CD) and sodium alginate/β-cyclodextrin immobilized carbon nanotubes (SA-β-CD/CNTs) hydrogel. Both hydrogels were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectral analysis, field emission scanning electron microscopy (FESEM), electron dispersive spectroscopy (EDX), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area analysis. The results showed SA-β-CD/CNTs hydrogel exhibits excellent thermal stability, high specific surface area and large porosity compared with SA-β-CD hydrogel. Batch experiments were performed to study the effect of several adsorptive variables such as initial concentration, pH, contact time and temperature. The adsorption performance of the prepared SA-β-CD/CNTs hydrogel was comprehensively reported with maximum percentage removal of up to 79.86% for SA-β-CD/CNTs and 69.54% for SA-β-CD. The optimum adsorption conditions were reported when the concentration of Ni(II) solution was maintained at 100 ppm, pH 5, 303 K, and contacted for 120 min with a 1000 mg dosage. The Freundlich isotherm and pseudo-second order kinetic model are the best fits to describe the adsorption behavior. A thermodynamic study was also performed. The probable interaction mechanisms that enable the successful binding of Ni(II) on hydrogels, including electrostatic attraction, ion exchange, surface complexation, coordination binding and host-guest interaction between the cationic sites of Ni(II) on both SA-β-CD and SA-β-CD/CNTs hydrogel during the adsorption process, were discussed. The regeneration study also revealed the high efficiency of SA-β-CD/CNTs hydrogel on four successive cycles compared with SA-β-CD hydrogel. Therefore, this work signifies SA-β-CD/CNTs hydrogel has great potential to remove Ni(II) from an aqueous environment compared with SA-β-CD hydrogel.

Adsorptive Behavior of Cu2+ and Benzene in Single and Binary Solutions onto Alginate Composite Hydrogel Beads Containing Pitch Pine-Based Biochar

In this study, we prepared alginate composite hydrogel beads containing various compositions of biochar produced from pitch pine (Pinus rigida) for the removal of Cu2+ and benzene from model pollutant solutions. The properties of the alginate/biochar hydrogel beads were evaluated using scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer−Emmet−Teller analyses. Adsorption behavior of alginate/biochar hydrogel beads indicated that the adsorption capacities for Cu2+ (28.6−72.7 mg/g) were enhanced with increasing alginate content, whereas the adsorption capacities for benzene (20.0−52.8 mg/g) were improved with increasing biochar content. The alginate/biochar hydrogel beads exhibited similar adsorption capacities for Cu2+ and benzene in the concurrent system with Cu2+ and benzene compared to those in a single pollutant system. Adsorption kinetics and isotherm studies of the alginate/biochar hydrogel beads followed the pseudo-second-order model (r2 = 0.999 for Cu2+, and r2 = 0.999 for benzene), and Langmuir model (r2 = 0.999 for Cu2+, and r2 = 0.995 for benzene). In addition, alginate/biochar hydrogel beads (containing 1 and 4% biochar) exhibited high reusability (>80%). Therefore, alginate/biochar hydrogel beads can be applied as adsorbents for the removal of multiple pollutants with different properties from wastewater.

Magnetic responsive mesoporous alginate/β-cyclodextrin polymer beads enhance selectivity and adsorption of heavy metal ions

Mesoporous (~7-8 nm) biopolymer hydrogel beads (HNTs-FeNPs@Alg/β-CD) were synthesised via ionic polymerisation route to separate heavy metal ions. The adsorption capacity of HNTs-FeNPs@Alg/β-CD was higher than that of raw halloysite nano tubes (HNTs), iron nanoparticles (FeNPs), and bare alginate beads. FeNPs induce the magnetic properties of adsorbent and metal-based functional groups in and around the hydrogel beads. The mesoporous surface of the adsorbent permits access of heavy metal ions onto the polymer beads to interact with internal active sites and the mesoporous polymer network. Maximum adsorption capacities of lead (Pb), copper (Cu), cadmium (Cd), and nickel (Ni) were 21.09 mg/g, 15.54 mg/g, 2.47 mg/g, and 2.68 mg/g, respectively. HNTs-FeNPs@Alg/β-CD was able to adsorb heavy metals efficiently (75-99%) under environment-relevant concentrations (200 μg/L) from mixed metal contaminants. The adsorption and selectivity trends of heavy metals were Pb > Cu > Cd > Ni, despite electrostatic binding strength of Cd > Cu > Pb > Ni and covalent binding strength of Pb > Ni > Cu > Cd. It demonstrated that not only chemosorption but also physisorption acts as the sorption mechanism. The reduction in surface area, porosity, and pore volume of the expended adsorbent, along with sorption study results, confirmed that pore filling and intra-particle diffusion played a considerable role in removing heavy metals.