Nano-FeS incorporated into stable lignin hydrogel: A novel strategy for cadmium removal from soil

Application of novel magnetic lignin hydrogels: Activated persulfate degrades pesticide contaminants

Lignin hydrogels have garnered significant attention due to their distinctive three-dimensional structures and potent swelling ability. In this work, a novel magnetic nanocomposite lignin hydrogel (MNLH) was fabricated through organic synthesis and solution immersion reduction. The obtained MNLH was used to activate persulfate(PDS) for pesticide degradation. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure and morphology of MNLH. The influence of factors such as the lignin hydrogel to nano-zero-valent iron (nZVI) and copper oxide (CuO) mass ratio, MNLH dosage, initial pH on the MNLH/PDS/imidacloprid (IMI) system. Remarkably, the MNLH/PDS/IMI system has a removal rate of up to 100%. Quenching and electron paramagnetic resonance (EPR) studies disclosed that the MNLH/PDS system degraded IMI through a combination of free radical and non-free radical pathways, with the latter being dominant. More importantly, in this study, the toxicity and hydrolysis sites of IMI were analyzed using ECOSAR and Gaussian09, respectively, confirming the feasibility of activating persulfate with MNLH. These findings underscore the potential of MNLH as a function material suitable for facilitating the persulfate-activated degradation of organic pollutants.

Efficient Pb(II) removal from contaminated soils by recyclable, robust lignosulfonate/polyacrylamide double-network hydrogels embedded with Fe2O3 via one-pot synthesis

Soil heavy metal removal strategies are increasingly valued for effectively reducing contamination and preventing secondary pollution. In this work, a double network hydrogel (Fe2O3@LH), consisting of lignosulfonate (LS) and polyacrylamide with embedded Fe2O3 nanoparticles, was synthesized successfully via a one-pot method and subsequently applied to adsorb lead (Pb) from contaminated soil. Incorporating Fe2O3 into the hydrogel enhances the adsorption capacity of Fe2O3@LH for Pb(II). The Fe2O3@LH hydrogel demonstrates a maximum Pb(II) adsorption capacity of 143.11 mg g-1, with Pb(II) removal mechanisms involving electrostatic adsorption, cation exchange, precipitation reactions, and the formation of coordination complexes, achieving a 22.3 % maximum removal efficiency in soil cultivation experiments. Additionally, the application of Fe2O3@LH markedly reduces the concentrations of cadmium (Cd) and arsenic (As) in the soil, meanwhile enhances the levels of total nitrogen (TN), soil organic matter (SOM), and cation exchange capacity (CEC) by 23.1 %, 10.6 %, and 16.9 %, respectively. Following 90 days of continuous application in the soil, the recovery rate of Fe2O3@LH remains above 75 %. The toxicity assay using zebrafish larvae indicates that Fe2O3@LH demonstrates good biosafety. This study demonstrates the considerable potential of Fe2O3@LH hydrogel for practical application in reducing Pb(II) levels in contaminated soil.

Self-separating core-shell spheres with a carboxymethyl chitosan/acrylic acid/Fe3O4 composite core for soil Cd removal

Cadmium (Cd) removal from soil is crucial as Cd enters the food chain and affect food safety, thus impose severe threaten to human health. We developed PPC@PC-Fe, a dual-functional core-shell sphere for efficient soil Cd reduction. The shell (PPC) was composed of encapsulated citric acid (CA) in a polylactic acid (PLA) and polyethylene glycol (PEG) network, which endows a function of activating Cd; and the core (PC-Fe) consisted of a polyacrylic acid/carboxymethyl chitosan (PAA/CMC) hydrogel with Fe3O4 nanoparticles to adsorb adjacent activated Cd. Upon water contact, the shell dissolved, releasing CA to activate soil Cd. Simultaneously, the swellable PC-Fe core absorbed water and expanded in size, promoting the disintegration of PLA in the shell, which triggered the automatic separation of core from shell, enabling the exposed PC-Fe core to rapidly adsorb Cd. Furthermore, the PC-Fe core can be magnetically removed after adsorption of Cd. Soil culture tests showed that 2 % PPC@PC-Fe reduced soil Cd from 6.009 mg/kg to 4.834 mg/kg in 10 days, with the acid-soluble Cd being the predominantly target to be activated and remove. This study demonstrates an effective stepwise activation and adsorption mechanism by a single carrier, with simple magnetic collection minimizing secondary pollution. It offers an innovative approach to the remediation of cadmium-contaminated sites in the field.

Effective and green in-situ remediation strategies based on TEMPO-nanocellulose/lignin/MIL-100(Fe) hydrogel nanocomposite adsorbent for lead and copper in agricultural soils

Hydrogel adsorbents are promising tools for reducing heavy metals' bioavailability in contaminated soil. However, their practical feasibility remains limited by the low stability, inefficient removal efficiency, and potential secondary pollution. Optimizing the adsorption operation and the functional properties of hydrogel adsorbents could eliminate this method's drawbacks. Herein, three innovative in-situ remediation strategies for Pb/Cu-contaminated soil were adopted based on the concept of novel TEMPO-cellulose (TO-NFCs)/lignin/acrylamide@MIL-100(Fe) nanocomposite hydrogel adsorbent (NCLMH). Characteristic analyses revealed ideal Pb/Cu adsorption mechanisms by swelling, complexation, electrical attraction, and ion exchange via carboxyl/hydroxyl/carbonyl groups and unsaturated Fe(III) sites on ANCMH besides FeOOH formation. The highest maximum theoretical adsorption capacities of Pb(II) and Cu(II) on ANCMH were 416.39 and 133.98 mg/g, under pH 6.5, governed by pseudo-second-order/Freundlich models. Greenhouse pot experiments with contaminated soils amended with two-depth layers of 0.5% NCLMHs (SA@NCLMH) displayed a decline in Pb and Cu bioavailability up to 85.9% and 74.5% within 45 d. Soil column studies simulating continuous water soil flushing coupled with NCLMH layers, instead of conventional extractant fluids, and connected to NCLMH-sand column as purification unit (CF@NCLMH) achieved higher removal rates for Pb, and Cu of 89.5% and 77.2% within 24 h. Alternatively, conducting multiple-pulse soil flushing mode (MF@NCLMH) gained the highest Pb and Cu removal of 96.5% and 85.4%, as the water flushing-stop flux events allowed adequate water movement/residence period, promoting Pb/Cu desorption-adsorption from soil to NCLMH. Also, the NCLMH-sand column conducting and easy separation of the stable/reusable NCLMHs prevented the potential secondary pollution. Interestingly, the three remediated soils reached the corresponding regulation of the permissible limits for Pb and Cu residential scenarios in medium-to-heavily agricultural polluted soils, alleviating the Pb/Cu bioaccumulation and phytotoxicity symptoms in cultivated wheat, especially after MF@NCLMH treatment. This study introduces promising alternative remediation strategies with high sustainability and feasibility in acidic-to-neutral heavy metal-contaminated agricultural soil.

Spatial heterogeneity of soil moisture caused by drainage and its effects on cadmium variation in rice grain within individual fields

Paddy drainage is the critical period for rice grain to accumulate cadmium (Cd), however, its roles on spatial heterogeneity of grain Cd within individual fields are still unknown. Herein, field plot experiments were conducted to study the spatial variations of rice Cd under continuous and intermittent (drainage at the tillering or grain-filling or both stages) flooding conditions. The spatial heterogeneity of soil moisture and key factors involved in Cd mobilization during drainages were further investigated to explain grain Cd variation. Rice grain Cd levels under continuous flooding ranged from 0.16 to 0.22 mg kg-1 among nine sampling sites within an individual field. Tillering drainage slightly increased grain Cd levels (0.19-0.31 mg kg-1) with little change in spatial variation. However, grain-filling drainage greatly increased grain Cd range to 0.33-0.95 mg kg-1, with a huge spatial variation observed among replicated sites. During two drainage periods, soil moisture decreased variously in different monitoring sites; greater variation (mean values ranged from 0.14 to 0.27 m3 m-3) was observed during grain-filling drainage. Accordingly, 2.9-3.3-fold variation in soil Eh and 0.55-0.67-unit variation in soil pH were observed among those sites. In the soil with low moisture, ferrous fractions such as ferrous sulfide (FeS) were prone to be oxidized to ferric fractions; meanwhile, the followed generation of hydroxyl radicals involved in Cd remobilization was enhanced. Consequently, soil dissolved Cd changed from 2.97 to 8.92 μg L-1 among different sampling sites during grain-filling drainage; thus, large variation was observed in grain Cd levels. The findings suggest that grain-filling drainage is the main process controlling spatial variation of grain Cd, which should be paid more attention in paddy Cd evaluation.

Multifaceted Hydrogel Scaffolds: Bridging the Gap between Biomedical Needs and Environmental Sustainability

Hydrogels are dynamically evolving 3D networks composed of hydrophilic polymer scaffolds with significant applications in the healthcare and environmental sectors. Notably, protein-based hydrogels mimic the extracellular matrix, promoting cell adhesion. Further enhancing cell proliferation within these scaffolds are matrix-metalloproteinase-triggered amino acid motifs. Integration of cell-friendly modules like peptides and proteins expands hydrogel functionality. These exceptional properties position hydrogels for diverse applications, including biomedicine, biosensors, environmental remediation, and the food industry. Despite significant progress, there is ongoing research to optimize hydrogels for biomedical and environmental applications further. Engineering novel hydrogels with favorable characteristics is crucial for regulating tissue architecture and facilitating ecological remediation. This review explores the synthesis, physicochemical properties, and biological implications of various hydrogel types and their extensive applications in biomedicine and environmental sectors. It elaborates on their potential applications, bridging the gap between advancements in the healthcare sector and solutions for environmental issues.

Calcium lignosulfonate-induced modification of soil chemical properties improves physiological traits and grain quality of maize (Zea mays) under salinity stress

Introduction

Salinity negatively affects maize productivity. However, calcium lignosulfonate (CLS) could improve soil properties and maize productivity.

Methods

In this study, we evaluated the effects of CLS application on soil chemical properties, plant physiology and grain quality of maize under salinity stress. Thus, this experiment was conducted using three CLS application rates, CLS0, CLS5, and CLS10, corresponding to 0%, 5%, and 10% of soil mass, for three irrigation water salinity (WS) levels WS0.5, WS2.5, and WS5.5 corresponding to 0.5 and 2.5 and 5.5 dS/m, respectively.

Results and discussion

Results show that the WS0.5 × CLS10 combination increased potassium (K 0.167 g/kg), and calcium (Ca, 0.39 g/kg) values while reducing the sodium (Na, 0.23 g/kg) content in soil. However, the treatment WS5.5 × CLS0 decreased K (0.120 g/kg), and Ca (0.15 g/kg) values while increasing Na (0.75 g/kg) content in soil. The root activity was larger in WS0.5 × CLS10 than in WS5.5 × CLS0, as the former combination enlarged K and Ca contents in the root while the latter decreased their values. The leaf glutamine synthetase (953.9 µmol/(g.h)) and nitrate reductase (40.39 µg/(g.h)) were higher in WS0.5 × CLS10 than in WS5.5 × CLS0 at 573.4 µmol/(g.h) and 20.76 µg/(g.h), leading to the improvement in cell progression cycle, as revealed by lower malonaldehyde level (6.57 µmol/g). The K and Ca contents in the leaf (881, 278 mg/plant), stem (1314, 731 mg/plant), and grains (1330, 1117 mg/plant) were greater in WS0.5 × CLS10 than in WS5.5 × CLS0 at (146, 21 mg/plant), (201, 159 mg/plant) and (206, 157 mg/plant), respectively. Therefore, the maize was more resistance to salt stress under the CLS10 level, as a 7.34% decline in yield was noticed when salinity surpassed the threshold value (5.96 dS/m). The protein (13.6 %) and starch (89.2 %) contents were greater in WS0.5 × CLS10 than in WS5.5 × CLS0 (6.1 %) and (67.0 %), respectively. This study reveals that CLS addition can alleviate the adverse impacts of salinity on soil quality and maize productivity. Thus, CLS application could be used as an effective soil amendment when irrigating with saline water for sustainable maize production.

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.

Functional Hydrogels Promote Vegetable Growth in Cadmium-Contaminated Soil

Over the years, the concentration of cadmium in soil has increased due to industrialization. Cadmium in the soil enters the human body through plant accumulation, seriously endangering human health. In the current study, two types of hydrogels were successfully synthesized using a free radical polymerization method: an ion-type hydrogel referred to as DMAPAA (N-(3-(Dimethyl amino) propyl) acrylamide)/DMAPAAQ (N,N-Dimethyl amino propyl acrylamide, methyl chloride quaternary) and a non-ion-type hydrogel known as DMAA (N,N-Dimethylacrylamide). In the experiment carried out in this study, the ion-type hydrogel DMAPAA/DMAPAAQ was introduced to cadmium-contaminated soil for vegetable cultivation. The study found that at cadmium levels of 0 and 2 mg/kg in soil, when exposed to a pH 2 solution, cadmium wasn't detected in the filtrate using ICP. As the amount of cadmium increased to 500 mg/kg, hydrogel addition gradually reduced the filtrate cadmium concentration. Notably, the use of the 4% hydrogel resulted in 0 mg/L of cadmium. For the 0% hydrogel, vegetable cadmium absorption was determined to be 0.07 mg/g, contrasting with 0.03 mg/g for the 4% hydrogel. The DMAPAA/DMAPAAQ hydrogel significantly boosts vegetable growth by efficiently absorbing nitrate ions through ion exchange, releasing them for plant uptake. In contrast, the DMAA hydrogel, used as a control, does not enhance plant growth despite its water absorption properties. In summary, the composite hydrogel shows great potential for enhancing vegetable yield and immobilizing heavy metals in soil.

Contaminated soil remediation with nano-FeS loaded lignin hydrogel: A novel strategy to produce safe rice grains while reducing cadmium in paddy field

Cadmium (Cd) contamination in agricultural soil has been an elevated concern due to the high health risks associated with the transfer through the soil-food chain, particularly in the case of rice. Recently, there has numerous researches on the use of nanoparticle-loaded materials for heavy metal-polluted soil remediation, resulting in favorable outcomes. However, there has been limited research focus on the field-scale application and recovery. This study was aimed to validate the Cd reduction effect of the nano-FeS loaded lignin hydrogel composites (FHC) in mildly polluted paddies, and to propose a field-scale application method. Hence, a multi-site field experiment was conducted in southern China. After the application for 94-103 days, the FHC exhibited a high integrity and elasticity, with a recovery rate of 91.90%. The single-round remediation led to decreases of 0.42-31.72% in soil Cd content and 1.52-49.11% in grain Cd content. Additionally, this remediation technique did not adversely impact rice production. Consequently, applying FHC in the field was demonstrated to be an innovative, efficient, and promising remediation technology. Simultaneously, a strategy was proposed for reducing Cd levels while cultivating rice in mildly polluted fields using the FHC.

Dual Benefits of Hydrogel Remediation of Cadmium-Contaminated Water or Soil and Promotion of Vegetable Growth under Cadmium Stress

This study aims to solve the problem of cadmium heavy metal ion pollution caused by the abuse of chemical fertilizers and activities such as mining, which pose a serious threat to the plant growth environment. We successfully synthesized DMAPAA (N-(3-(Dimethyl amino) propyl) acrylamide)/DMAPAAQ (N, N-Dimethyl amino propyl acrylamide, methyl chloride quaternary) hydrogels via free radical polymerization. Subsequently, we conducted experiments on this hydrogel for growing vegetables under cadmium stress conditions in aqueous solutions and soil. The cadmium capture capacity of DMAPAA/DMAPAAQ hydrogels under different cadmium ion concentrations and pH values was evaluated by using inductively coupled plasma optical emission spectrometry (ICP). The research results show that under the condition of pH = 7.3, the cadmium capture capacity of DMAPAA/DMAPAAQ hydrogels is the greatest. We used the Langmuir model to fit the adsorption data, and the correlation coefficient was as high as 0.96, indicating that the model fits well. The application of the hydrogels promoted the growth of vegetables in soil under cadmium stress conditions. The results showed that when the added amount of hydrogel was 4%, the dry weight of the vegetables was the largest. In addition, when the added amount of cadmium was 500 mg/kg and the added amount of hydrogel was 4%, the absorption of cadmium by the vegetables decreased to an undetectable level. In summary, the hydrogel successfully synthesized in this study can be effectively used to immobilize cadmium ions in soil while positively promoting the growth and yield of vegetables. This achievement has practical significance for solving the problem of heavy metal ion pollution.

Potential functions of engineered nanomaterials in cadmium remediation in soil-plant system: A review

Soil cadmium (Cd) contamination is a global environmental issue facing agriculture. Under certain conditions, the stable Cd that bound to soil particles tend to be remobilized and absorbed into plants, which is seriously toxic to plant growth and threat food safety. Engineering nanomaterials (ENMs) has attracted increasing attentions in the remediation of Cd pollution in soil-plant system due to their excellent properties with nano-scale size. Herein, this article firstly systematically summarized Cd transformation in soil, transport in soil-plant system, and the toxic effects in plants, following which the functions of ENMs in these processes to remediate Cd pollution are comprehensively reviewed, including immobilization of Cd in soil, inhibition in Cd uptake, transport, and accumulation, as well as physiological detoxication to Cd stress. Finally, some issues to be further studied were raised to promote nano-remediation technology in the environment. This review provides a significant reference for the practical application of ENMs in remediation of Cd pollution in soil, and contributes to sustainable development of agriculture.

A novel biochar-based composite hydrogel for removing heavy metals in water and alleviating cadmium stress in tobacco seedlings

A novel composite hydrogel (AM/CMC/B) synthesized from peanut shell biochar effectively adsorbs heavy metal Cd in water and reduces its toxicity to tobacco seedlings. The hydrogel, prepared via hydrothermal polymerization using acrylamide (AM), carboxymethyl cellulose (CMC), and peanut shell biochar (B), exhibited a maximum adsorption capacity of 164.83 mg g-1 for Cd2+ and followed a pseudo-second-order kinetic model. In pot experiments, the application of exogenous AM/CMC/B mitigated the inhibitory effects of Cd-contaminated soil on tobacco seedling growth. Addition of 10 mg kg-1 Cd resulted in improved phenotype, root system development, enhanced photosynthetic capacity, stomatal conductance (Gs), stomatal number, and increased antioxidant activity while reducing MDA content and leaf cell death. These findings highlight the potential of AM/CMC/B as an environmentally friendly adsorbent for Cd removal from water and for reducing Cd stress toxicity in tobacco and other plants.

Hydrogel-potassium humate composite alleviates cadmium toxicity of tobacco by regulating Cd bioavailability

Cadmium (Cd) removal from soil to reduce Cd accumulation in plants is essential for agroecology, food safety, and human health. Cd enters plants from soil and affects plant growth and development. Hydrogels can easily combine with Cd, thereby altering its bioavailability in soil. However, few studies have evaluated the effects of hydrogel on the complex phytotoxicity caused by Cd uptake in plants and the microbial community structure. Herein, a new poly (acrylic acid)-grafted starch and potassium humate composite (S/K/AA) hydrogel was added to soil to evaluate its impact on tobacco growth and the soil microenvironment. The results indicate that the addition of S/K/AA hydrogel can significantly improve the biomass, chlorophyll (Chl) content, and photosynthetic capacity of tobacco plants during Cd stress conditions, and decrease Cd concentration, probably by affecting Cd absorption through the expression of Cd absorption transporters (e.g., NRAMP5, NRAMP3, and IRT1). Moreover, the application of S/K/AA hydrogel not only reduced the accumulation of reactive oxygen species (ROS), but also reduced the antioxidant activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), suggesting that S/K/AA hydrogel alleviates Cd toxicity via a non-antioxidant pathway. Notably, we further analyzed the effectiveness of the hydrogel on microbial communities in Cd-contaminated soil and found that it increased the Cd-tolerant microbial community (Arthrobacter, Massilia, Streptomyces), enhancing the remediation ability of Cd-contaminated soil and helping tobacco plants to alleviate Cd toxicity. Overall, our study provides primary insights into how S/K/AA hydrogel affects Cd bioavailability and alleviates Cd toxicity in plants.

Oxidative compensation mechanism of Fe-S synergetic inhibition of Cd activity in paddy field during flooding and drainage

It is known that the transformation of Fe and S forms in soil affects the migration and activity of Cd, but the coordinated regulation of Cd activity by Fe and S under different redox conditions is still unclear. Here, Diffusive gradients in thin films (DGT), an in-situ monitoring technique, is used to explore the difference of the regulation of Cd activity in paddy fields with ferrihydrite (FH) and ferrihydrite coprecipitated by sulfate (FH-S) under the flooding and drainage conditions. The addition of FH-S and FH significantly reduced the activity of Cd (Dissolved, Exchanged, and CDGT-Cd). Compared with pure FH, the adsorption extent of Cd in FH was enhanced by increasing concentrations of SO42- (i.e., S/Fe ratio), which is attributed to the decrease in the crystallinity of FH by sulfate. During soil flooding, the addition of FH-S promoted the production of metal sulfide (CdS and FeS/FeS2). The activity of Cd increased after drainage, while the FH-S treatment groups delayed the release of Cd. After 30 days of drainage, the concentration of Cd in FH-S treatment groups decreased by 28.9-44.1 % compared with the control group. The fresh FeS/FeS2 is not the main adsorbent for fixing Cd, and due to the existence of oxidation compensation mechanism, the preferential oxidation of FeS/FeS2 delays the release of Cd in the drainage stage. Our study shed new light on the mechanism of Fe-S synergistic regulation of Cd and remediation of Cd-contaminated soils.

Synthesis of magnetic sodium lignosulfonate hydrogel(Fe3O4@LS) and its adsorption behavior for Cd2+ in wastewater

Heavy metal pollution is becoming increasingly serious. Heavy metal pollutants are nonbiodegradable and can be bioenriched through the food chain, and thus, they greatly threaten the environment and human health. Hydrogels, as an ideal adsorbent, have been widely used to treat heavy metal industrial wastewater. Sodium lignosulfonate hydrogel (LS) was prepared by free-radical grafting copolymerization, and nano-Fe3O4 particles were loaded in LS by an in-situ precipitation method (Fe3O4@LS). The magnetic properties and adsorption capacity of Fe3O4@LS are closely related to the load capacity of Fe3O4. XRD, FTIR, XPS, SEM, TEM, BET, and TGA analyses of the materials were performed. Subsequently, the removal effect of the typical pollutant Cd2+ in heavy metal-polluted water was studied with Fe3O4@LS as the adsorbent. The influences of the Fe3O4@LS dosage and initial pH were investigated, and the adsorption kinetics and thermodynamics were further explored and discussed. Finally, the adsorption mechanism of Fe3O4@LS on Cd2+ was obtained. Results show that Fe3O4@LS has a more stable spatial network structure than LS, and the pore size, specific surface area and active sites increase. The maximum adsorption capacity can reach 88.00 mg/g when pH = 6 and the dosage of Fe3O4@LS is 1000 mg/L. The adsorption of Cd2+ by Fe3O4@LS conforms to pseudosecond-order kinetics and the Temkin isothermal adsorption model. Further mechanistic investigations show that the sorption of Cd2+ on Fe3O4@LS is mainly attributed to surface complexation, electrostatic attraction and coprecipitation. The coexistence of cations in water will inhibit the adsorption of Fe3O4@LS. Fe3O4@LS has superparamagnetism and a good response to an external magnetic field. The adsorption rate can still reach >60 % after four elutions with NaCl as the eluent. This material can be reused and has good application potential.

Adsorption of lead ions by activated carbon doped sodium alginate/sodium polyacrylate hydrogel beads and their in-situ recycle as sustainable photocatalysts

In this study, sodium alginate (SA), sodium polyacrylate (PAAS) and powdered activated carbon (PAC) were cross-linked by calcium ions [(Ca(II)] to form SA/PAAS/PAC (SPP) hydrogel beads. The hydrogel-lead sulfide (SPP-PbS) nanocomposites were successfully synthesized by in-situ vulcanization after the lead ions [(Pb(II)] adsorption. SPP showed an optimal swelling ratio (600% at the pH value of 5.0) and superior thermal stability (206 °C of heat-resistance index). The adsorption data of Pb(II) was compatible with the Langmuir model, and the maximum adsorption capacity of SPP was 391.65 mg/g after optimizing the mass ratio of SA to PAAS (3:1). The addition of PAC not only enhanced the adsorption capacity and stability, but also promoted photodegradation. The significant dispersive capacity of PAC and PAAS resulted in PbS nanoparticles with particle sizes of around 20 nm. SPP-PbS showed good photocatalysis and reusability. The degradation rate of RhB (200 mL, 10 mg/L) was 94% within 2 h and maintained above 80% after 5 cycles. The treatment efficiency of SPP was more than 80% in actual surface water. The results of quenching experiments and electron spin resonance (ESR) experiments revealed that the superoxide radicals (O₂^-) and holes (h⁺) were the main active species in the photocatalytic process.

Current roles of lignin for the agroindustry: Applications, challenges, and opportunities

Lignin has the potential to be used as an additive, coating agent, fertilizer, plant growth stimulator, and packaging material in the agroindustry due to its functional aromatic structure. The quantitative measurement of functional groups is a significant element of the research for lignin structure since they directly impact their optical, dispersion, and chemical properties. These physical and chemical properties of lignin strongly depend on its type and source and its isolation procedure. Thus, lignin provides numerous opportunities for the circular economy in the agroindustry; however, studying and resolving the challenges associated with its separation, purification, and modification is required. This review discusses the most recent findings on lignin use in agroindustry and historical facts about lignin. The properties of lignin and its roles as coating agents, pesticide carriers, plant growth stimulators, and soil-improving agents have been summarized. The emerging challenges in the field of lignin-based agroindustry are considered, and potential future steps to overcome these challenges are discussed.

Enhanced hybrid hydrogel based on wheat husk lignin-rich nanocellulose for effective dye removal

Polyvinyl alcohol (PVA) hydrogels were enhanced mechanically through the addition of lignin-rich nanocellulose (LCN), soluble ash (SA) and montmorillonite (MMT) for dye removal. The hybrid hydrogels reinforced with 33.3 wt% of LCN had a 163.0% increase in storage modulus as compared to the PVA/0LCN-33.3SM hydrogel. LCN can be added to the PVA hydrogel to alter its rheological properties. Additionally, hybrid hydrogels were highly efficient in removing methylene blue from wastewater, which was attributed to the synergistic effects of the PVA matrix supporting embedded LCN, MMT, and SA. The adsorption time (0–90 min) showed that the hydrogels containing MMT and SA had high removal efficiency, and the adsorption of methylene blue (MB) by PVA/20LCN-13.3SM was greater than 95.7% at 30°C. It was found that MB efficiency decreased with a high MMT and SA content. Our study provided a new method for the fabrication of polymers-based eco-friendly, low-cost and robust physical hydrogels for the MB removal.

Properties and mechanism of Cr(VI) removal by a ZnCl2-modified sugarcane bagasse biochar-supported nanoscale iron sulfide composite

A ZnCl₂-modified biochar-supported nanoscale iron sulfide composite (FeS-ZnBC) was successfully prepared to address the easy oxidization of FeS and enhance Cr(VI) removal from water. The material was characterized by SEM, XRD, FTIR, and XPS. The effects of FeS:ZnBC mass ratio, FeS-ZnBC dosage, solution pH, initial Cr(VI) concentration, and reaction time on the adsorption performance were investigated. The results revealed that the optimum adsorption capacity of FeS-ZnBC (FeS:ZnBC = 1:2) for Cr(VI) was 264.03 mg/g at 298 K (pH = 2). A Box-Behnken design (BBD) was applied to optimize the input variables that affected the adsorption of Cr(VI) solution. The results revealed that the highest removal (99.52%) of Cr(VI) solution was achieved with a Cr(VI) initial concentration of 150.59 mg/L, FeS-ZnBC adsorbent dosage of 2 g/L, and solution pH of 2. The sorption kinetics could be interpreted using a pseudo-second-order kinetic model. The isotherms were simulated using the Redlich-Peterson isotherm model, indicating that Cr(VI) removal by the FeS-ZnBC composites was a hybrid chemical reaction-sorption process. The main mechanisms of Cr(VI) removal by FeS-ZnBC were adsorption, chemical reduction, and complexation. This study demonstrated that FeS-ZnBC has potential application prospects in Cr(VI) removal.

The strategic applications of natural polymer nanocomposites in food packaging and agriculture: Chances, challenges, and consumers' perception

Natural polymer-based nanocomposites have received significant attention in both scientific and industrial research in recent years. They can help to eliminate the consequences of application of petroleum-derived polymeric materials and related environmental concerns. Such nanocomposites consist of natural biopolymers (e.g., chitosan, starch, cellulose, alginate and many more) derived from plants, microbes and animals that are abundantly available in nature, biodegradable and thus eco-friendly, and can be used for developing nanocomposites for agriculture and food industry applications. Biopolymer-based nanocomposites can act as slow-release nanocarriers for delivering agrochemicals (fertilizers/nutrients) or pesticides to crop plants to increase yields. Similarly, biopolymer-based nanofilms or hydrogels may be used as direct product coating to extend product shelf life or improve seed germination or protection from pathogens and pests. Biopolymers have huge potential in food-packaging. However, their packaging properties, such as mechanical strength or gas, water or microbial barriers can be remarkably improved when combined with nanofillers such as nanoparticles. This article provides an overview of the strategic applications of natural polymer nanocomposites in food and agriculture as nanocarriers of active compounds, polymer-based hydrogels, nanocoatings and nanofilms. However, the risk, challenges, chances, and consumers' perceptions of nanotechnology applications in agriculture and food production and packaging have been also discussed.

Foliar Application of Reaction Products Derived from Selenite Removal by Iron Monosulfide for Brassica rapa ssp. Chinensis L

The extensive application of FeS in environmental remediation requires the recovery and reuse of reaction products between FeS and pollutants. Therefore, foliar application of reaction products derived from selenite [Se(IV)] removal by FeS for pak choi was performed. The removal rate of Se(IV) by 100 mg/L FeS was 0.047 h^-1. 93.2% of Se(IV) was reduced to Se(0), and FeS was correspondingly oxidized to goethite (78.9%), lepidocrocite (21.1%), and S(0) (91.5%) based on the analysis of X-ray absorption fine structure. The reaction products promoted the growth of pak choi in terms of fresh biomass, vitamin C, and protein, ascribed to the key roles of Fe and S in enhancing the electron transfer rate and light conversion rate. Furthermore, the application of reaction products decreased by 64% of disease incidence as compared with the pathogen Pseudomonas syringae pv. maculicola-infected control. The total Se content in plants increased to 576 μg/kg and was composed of 11.9% of SeMeCys, 29.8% of SeMet, and 58.3% of SeCys after exposure to reaction products, which is beneficial to the human dietary intake from pak choi. This study demonstrated that the reaction products between FeS and Se(IV) could be recovered and applied as a nano-enabled strategy to prevent crop insecurity.

Titanium dioxide nanoparticles decreases bioconcentration of azoxystrobin in zebrafish larvae leading to the alleviation of cardiotoxicity

Interactions between titanium dioxide nanoparticles (n-TiO₂) and pollutants in the aquatic environment may alter the bioavailability of pollutants, and thus altering their toxicity and fate. In order to investigate the bioconcentration of azoxystrobin (AZ) and its mechanism of cardiotoxicity in the presence of n-TiO₂, the experiment was divided into control, n-TiO₂ (100 μg/L), AZ (40, 200 and 1000 μg/L) and AZ (40, 200, 1000 μg/L) + n-TiO₂ groups, and the zebrafish embryos were exposed to the exposure solution until 72 h post-fertilization. Results suggested the presence of n-TiO₂ notably reduced the accumulation of AZ in larvae compared with exposure to AZ alone, thereby significantly decreasing AZ-induced cardiotoxicity, including heart rate changes, pericardium edema, venous thrombosis, increased sinus venosus and bulbus arteriosus distance and changes in cardiac-related gene expression. Further studies showed that AZ + n-TiO₂ together restrained total-ATPase and Ca²⁺-ATPase activities, while the activity of Na⁺K⁺-ATPase increased at first and then decreased. Furthermore, there were significant changes in the expressions of oxidative phosphorylation and calcium channel-related genes, suggesting mitochondrial dysfunction may be the potential mechanism of cardiotoxicity induced by AZ and n-TiO₂. This study supplies a new perspective for the joint action of AZ and environmental coexisting pollutants and provides a basis for ecological risk management of pesticides.

Cr(VI) immobilization in soil using lignin hydrogel supported nZVI: Immobilization mechanisms and long-term simulation

A novel nanocomposite, named as nZVI@LH, was prepared by nanoscale zero-valent iron (nZVI) supported on lignin hydrogel and was used in the remediation of Cr(VI)-contaminated soil collected from an industrial site. Meanwhile, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray diffractometry (XRD) results determined that nZVI nanoparticles disperse uniformly on hydrogel. After the 14 days remediation, the immobilization efficiency of Cr(VI) could reach over 87% in the treatment of 3% (w/w%) nZVI@LH and 26% in the treatment of bare-nZVI. Leaching experiment results showed that the treatment group with 3% (w/w%) nZVI@LH was up to the national leaching toxicity identification standard, and there was no threat in simulation of acid rain over the long term. The water-soluble (WS) fraction in 3^# nZVI@LH treatment decreased 31.1%, while the Fe-Mn oxide bound (OX) fraction and organic matter-bound (OM) fraction increased 10.9% and 13.4%, respectively. Moreover, nZVI@LH had limited impact on soil properties and the capability to immobilize Cr over a long period exposure to acid rain. This work prove that nZVI@LH has the potential to remediate Cr contaminated soil. Furthermore, details of possible mechanistic insight into the Cr remediation were carefully discussed.

Effects of Carbonaceous Materials with Different Structures on Cadmium Fractions and Microecology in Cadmium-Contaminated Soils

Carbonaceous materials have proved to be effective in cadmium remediation, but their influences on soil microecology have not been studied well. Taking the structural differences and the maintenance of soil health as the entry point, we chose graphene (G), multi-walled carbon nanotubes (MWCNTs), and wetland plant-based biochar (ZBC) as natural and engineered carbonaceous materials to explore their effects on Cd fractions, nutrients, enzyme activities, and microbial communities in soils. The results showed that ZBC had stronger electronegativity and more oxygen-containing functional groups, which were related to its better performance in reducing soil acid-extractable cadmium (EX-Cd) among the three materials, with a reduction rate of 2.83-9.44%. Additionally, ZBC had greater positive effects in terms of improving soil properties, nutrients, and enzyme activities. Redundancy analysis and correlation analysis showed that ZBC could increase the content of organic matter and available potassium, enhance the activity of urease and sucrase, and regulate individual bacterial abundance, thereby reducing soil EX-Cd. Three carbonaceous materials could maintain the diversity of soil microorganisms and the stability of the microbial community structures to a certain extent, except for the high-dose application of ZBC. In conclusion, ZBC could better immobilize Cd and maintain soil health in a short period of time.

Competition adsorption of malachite green and rhodamine B on polyethylene and polyvinyl chloride microplastics in aqueous environment

Microplastics (MPs) will cause compound pollution by combining with organic pollutants in the aqueous environment. It is important for environmental protection to study the adsorption mechanism of different MPs for pollutants. In this study, the adsorption behaviors of malachite green (MG) and rhodamine B (RhB) on polyethylene (PE) and polyvinyl chloride (PVC) were studied in single systems and binary systems, separately. The results show that in single system, the adsorptions of between MPs for pollutants (MG and RhB) are more consistent with the pseudo-second-order kinetics and Freundlich isotherm model, the adsorption capacity of both MPs for MG is greater than that of RhB. The adsorption capacities of MG and RhB were 7.68 mg/g and 2.83 mg/g for PVC, 4.52 mg/g and 1.27 mg/g for PE. In the binary system, there exist competitive adsorption between MG and RhB on MPs. And the adsorption capacities of PVC for the two dyes are stronger than those of PE. This is attributed to the strong halogen-hydrogen bond between the two dyes and PVC, and the larger specific surface area of PVC. This study revealed the interaction and competitive adsorption mechanism between binary dyes and MPs, which is of great significance for understanding the interactions between dyes and MPs in the multi-component systems.

A novel lignin hydrogel supported nZVI for efficient removal of Cr(VI)

A novel hydrogel-supported nanoscale zero-valent iron (nZVI) composite (nZVI@LH) was synthesized by ion exchange and in-situ reduction. The removal efficiency was tested, and the mechanism was also explored. The nZVI@LH at the precursor Fe(II) ion concentration of 0.1 mol/L presented an enhanced Cr(VI) removal capacity of 310.86 mg/g Fe⁰ at pH 5.3, which was 11.6 times more than that of the pure nZVI. The removal efficiency of the composite at pH 2.1 was more than double compared with alkaline or neutral conditions. Scanning electron microscopy (SEM) suggested that the nZVI particles were uniformly immobilized in the lignin hydrogel. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) provided evidence supporting the removal mechanism. According to the XPS results, the high removal capacity of the composite was attributed to chemical reduction/precipitation (69.7%), surface sorption (19.7%), and swelling uptake (10.6%). The pseudo-first-order reduction kinetics and pseudo-second-order kinetic model were employed to simulate the kinetic data, which supported the mechanism that chemical reduction and surface sorption could simultaneously remove Cr(VI). The electron acceptor and electron donor affected the reaction rate, and the presence of humic acid significantly inhibited the reaction. The present study demonstrated that lignin hydrogel acted as a carrier to prevent aggregation of nZVI particles. nZVI particles loaded on lignin hydrogel showed high reactivity and high degree of utilization compared with bare-nZVI. These results exhibited the great potential of nZVI@LH in practical water treatment due to its high activity.

Antimicrobial and Anti-Inflammatory Activity of Low-Energy Assisted Nanohydrogel of Azadirachta indica Oil

Plant-based bioactive compounds have been utilized to cure diseases caused by pathogenic microorganisms and as a substitute to reduce the side effects of chemically synthesized drugs. Therefore, in the present study, Azadirachta indica oil nanohydrogel was prepared to be utilized as an alternate source of the antimicrobial compound. The total phenolic compound in Azadirachta indica oil was quantified by chromatography analysis and revealed gallic acid (0.0076 ppm), caffeic acid (0.077 ppm), and syringic acid (0.0129 ppm). Gas chromatography−mass spectrometry analysis of Azadirachta indica oil revealed the presence of bioactive components, namely hexadecenoic acid, heptadecanoic acid, ç-linolenic acid, 9-octadecanoic acid (Z)-methyl ester, methyl-8-methyl-nonanoate, eicosanoic acid, methyl ester, and 8-octadecane3-ethyl-5-(2 ethylbutyl). The nanohydrogel showed droplet size of 104.1 nm and −19.3 mV zeta potential. The nanohydrogel showed potential antimicrobial activity against S. aureus, E. coli, and C. albicans with minimum inhibitory, bactericidal, and fungicidal concentrations ranging from 6.25 to 3.125 (µg/mL). The nanohydrogel showed a significantly (p < 0.05) higher (8.40 log CFU/mL) value for Gram-negative bacteria E. coli compared to Gram-positive S. aureus (8.34 log CFU/mL), and in the case of pathogenic fungal strain C. albicans, there was a significant (p < 0.05) reduction in log CFU/mL value (7.79−6.94). The nanohydrogel showed 50.23−82.57% inhibition in comparison to standard diclofenac sodium (59.47−92.32%). In conclusion, Azadirachta indica oil nanohydrogel possesses great potential for antimicrobial and anti-inflammatory activities and therefore can be used as an effective agent.

Removal of heavy metal(loid)s from aqueous solution by biogenic FeS-kaolin composite: Behaviors and mechanisms

In this work, a green adsorbent, biogenic FeS-kaolin composite (KL-FeS) was synthesized by sulfate-reducing bacteria (SRB) mediation, and its potential for Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) removal was evaluated. Among prepared composites, the KL-FeS synthesized at a concentration of 2 g/L kaolin performed a better removal efficiency on heavy metal(loid)s and the adsorption results followed the pseudo-second-order and Redlich-Peterson models, indicating that the adsorption was a hybrid chemical reaction-adsorption process. Additionally, the maximum adsorption capacities of Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) on KL-FeS in monocomponent system were 71.71, 133.54, 51.90, 54.41, 38.71 and 96.38 mg/g, respectively (pH = 5.0 ± 0.1, T = 25 °C). In addition, the increase of pH and ionic strength promoted the adsorption capacities of KL-FeS for metal-(loid)s. Moreover, FTIR, XPS and XRD analyses supported that surface complexation, hydrogen bonding, ion exchange, electrostatic interaction and chemical precipitation were predominately mechanisms involved in the adsorption process. Furthermore, KL-FeS displayed higher affinity for Pb(II), Sb(III) and Cu(II) in the multi-component system. This work highlighted the potential of biogenic FeS-kaolin composite for simultaneous removal of multiple heavy metal(loid)s under aerobic conditions.

The symbiotic system of sulfate-reducing bacteria and clay-sized fraction of purplish soil strengthens cadmium fixation through iron-bearing minerals

The microbe-clay mineral system is widely known to reduce the fluidity of heavy metals through biomineralization, thus mitigating soil pollution stemming from heavy metals. Here, we investigated the effect of mineral distinction on the solidification of cadmium (Cd) using sulfate-reducing bacteria (SRB) to construct symbiotic systems with purplish soil, clay-sized fraction of purple soil (Clay_-csp), clay particles of amorphous iron (Fe) oxide (Clay_-ox), clay particles removing crystalline Fe oxide (Clay_-CBD), and residues of Clay_-CBD treated by hydrochloric acid (Clay_-HCl). The difference in Cd morphology among purplish soil, Clay_-csp, and Clay_-ox indicated that the fixation of Cd in soil was largely determined by Fe oxides. The content of Cd in Clay_-csp decreased by 66.7% after the removal of amorphous Fe, confirming that clay easily adsorbed infinitive Fe oxides in purple soil. In the system of SRB and Clay_-ox, carbonate-bound Cd (F2) decreased by 14.85% and residual Cd (F5) increased by 14% from the retardation to late decline phase, eventually forming iron-sulfur (Fe-S) compounds. Based on the correlation analyses of Cd and Fe in amorphous-bound state and Fe-manganese (Mn) oxidation state in simulation experiments, it is demonstrated that Fe-Mn oxides control the behavior of Cd in soil clay, and SRB-mediated Fe-bearing minerals promote the transformation of Cd from activated to stable state.

Adsorption mechanism of two pesticides on polyethylene and polypropylene microplastics: DFT calculations and particle size effects

Polyethylene (PE) and polypropylene (PP) microplastics (MPs), as carriers, can bind with pesticides, which propose harmful impacts to aqueous ecosystems. Meanwhile, carbofuran and carbendazim (CBD), two widely used carbamate pesticides, are toxic to humans because of the inhibition of acetylcholinesterase activity. The interaction between two MPs and two pesticides could start in farmland and be maintained during transportation to the ocean. Herein, the adsorption behavior and mechanism of carbofuran and carbendazim (CBD) by PE and PP MPs were investigated via characterization and density functional theory (DFT) simulation. The adsorption kinetic and thermodynamic data were best described by pseudo-second-order kinetics and the Freundlich models. The adsorption behaviors of individual carbofuran/CBD on both MPs were very similar. The CBD adsorption rate and capacity of PE and PP MPs were higher than those of carbofuran. This phenomenon explained the lower negative effects of DOM (oxalic acid, glycine (Gly)) on CBD adsorption relative to those of carbofuran. The presence of oxalic acid and Gly decreased the PE adsorption by 20.40-48.02% and the PP adsorption by 19.27-42.11%, respectively. It indicated the significance of DOM in carbofuran cycling. The adsorption capacities were negatively correlated with MPs size, indicating the importance of specific surficial area. Fourier transformation infrared spectroscopy before and after adsorption suggested that the adsorption process did not produce any new covalent bond. Instead, intermolecular van der Waals forces were one of the primary adsorption mechanisms of carbofuran and CBD by MPs, as evidenced by DFT calculations. Based on the zeta potential, the electrostatic interaction explained the higher adsorption CBD by MPs than carbofuran.

Immobilization of cadmium in contaminated soils using sulfidated nanoscale zero-valent iron: Effectiveness and remediation mechanism

Sulfidated nanoscale zero-valent iron (S-nZVI) has shown excellent removal capacity for the removal of cadmium (Cd) in aqueous phase. Herein, the effectiveness and the mechanism of S-nZVI for the remediation of Cd contaminated soil were investigated for the first time. The results of sequential extraction procedures (SEP) showed that the exchangeable (EX) Cd was decreased by over 97.6% at the optimal dosage of 5 g kg^-1 S-nZVI during 30 d incubation and converted to less available Cd such as iron-manganese oxides-bound (OX) and organic matter-bound (OM) fractions. pH has negligible effect on the immobilization of Cd in soil, since OX fraction was stabilized in the range of 72-92% at initial soil pH range from 5.3 to 7.5. SEM-EDS analysis of the separated magnetic particles implied that Cd was successfully enriched on S-nZVI and the distribution of Cd was closely related to Fe, S, and O. CdO and CdS was confirmed as the key products for Cd immobilization in soil. Meanwhile, the S-nZVI was oxided to α-FeOOH, γ-FeOOH, and γ-Fe₂O₃. The existence of CdO was visibly related to the iron oxides, suggesting the synergetic immobilization effect by iron oxides. Overall, S-nZVI was promising for the remediation of Cd-contaminated soil.

Removal of cadmium and tetracycline by lignin hydrogels loaded with nano-FeS: Nanoparticle size control and content calculation

Cadmium (Cd) and tetracycline (TC) cause serious environmental risks. Nanomaterials have been extensively applied for environmental remediation. The size and content of nanoparticles directly affect the removal of contaminants. However, size regulation and quantitative determination of nanoparticles cannot be easily realized. In this study, hydrogels with different polymerization degrees were prepared by adjusting the contents of acrylamide (AM) and sodium lignosulfonate polymeric monomers. Ferrous sulfide (FeS) nanoparticles of different sizes were synthesized in situ within the hydrogels. The nanoparticle size decreased from 600 to 200 nm with increasing hydrogel polymerization degree, and an incomplete crystalline state was observed at the highest polymerization degree. By combining energy dispersive spectroscopy (EDS) images with the maximum between-class variance (Otsu) method, the content of nanoparticles was calculated to be 7.81%, 15.05%, 22.62%, 27.10%, 21.97%, and 23.95%. The distribution state of FeS compounds was also obtained. A low polymerization degree resulted in high FeS dispersal, and a high polymerization degree affected the uniformity distribution based on irregular ion diffusion. The obtained nanocomposites with different polymerization degrees were applied to the removal of Cd and TC in water. The removal capacity for both contaminants revealed a trend of initially increasing and then decreasing. The initial increase was related to the increasing content and decreasing size of the FeS nanoparticles, while the following decrease was due to the decreasing content and incomplete crystallization of the FeS nanoparticles. Overall, changing the proportion of polymeric monomers is an effective way to regulate particle size, and the Otsu method combined with EDS mapping images is a feasible method for calculating the content of nanoparticles.

Recent advances in lignin-based porous materials for pollutants removal from wastewater

Water pollution is one of the most serious threats facing mankind today and has obtained widespread attention. Significant advances have been made in the past decades to apply porous materials in wastewater treatment, due to their large specific surface areas (S_BET) for interaction with the aimed ions or molecules. However, the majority of porous materials are prepared from fossil-based resources and still possess some drawbacks, such as high cost and non-degradability, which inevitably cause secondary pollution to the environment from their production to disposal. Lignin is the most abundant and the only scalable renewable aromatic resource on earth. Due to its unique physicochemical properties including high carbon content, plentiful functional groups and environmental friendliness, the lignin-based porous materials (LPMs) have shown promising prospects in efficient removal of soluble pollutants from wastewater. In this review, we firstly described the structural and chemical basis of LPMs, following presented the recent progress in the decontamination of heavy metal ions, organic dyes, antibiotics, anions and radionuclides from aqueous systems. Additionally, the outlook was provided to promote more practical implementation of LPMs in the near future.

Cadmium isotopic fractionation in lead-zinc smelting process and signatures in fluvial sediments

Cadmium (Cd) is a toxic heavy metal pollutant. Various industrial activities, especially metal smelting, are the main sources of Cd pollution. Cd isotopes have exhibited the ability to be excellent source tracers and can be used to assess the pollution contributions from different sources. Herein, in a typical lead-zinc smelter, Shaoguan, China, significant Cd isotopic fractionation was found during the high temperature smelting process and followed a Rayleigh distillation model. The heavier Cd isotopes were concentrated in the slag, while the lighter Cd isotopes were concentrated in the dust. In the downstream sediment profile of the smelter, sediments have extremely high Cd concentrations that far exceed the Chinese background sediment, indicating severe pollution levels. The ε^114/110Cd of the sediment core, ranged from - 0.62 ± 0.5-1.73 ± 0.5, are found between slag (ε^114/110Cd=10.42) and dust (ε^114/110Cd=-5.68). The binary mixture model suggests that 88-93% of the Cd in sediment profile was derived from the slag, and 7-12% from the deposition of dust. The findings demonstrate the great potential to apply Cd isotopes as a new geochemical tool to distinguish anthropogenic sources and quantify the contribution from various sources in the environment.

Research progress and mechanism of nanomaterials-mediated in-situ remediation of cadmium-contaminated soil: A critical review

Cadmium contamination of soil is a global issue and in-situ remediation technology as a promising mitigation strategy has attracted more and more attention. Many nanomaterials have been applied for the in-situ remediation of cadmium-contaminated soil due to their excellent properties of the nano-scale size effect. In this work, recent research progress of various nanomaterials, including carbon nanomaterials, metal-based nanomaterials and nano mineral materials, in the removal of cadmium and in-situ remediation of cadmium-contaminated soil were systematically discussed. Additional emphases were particularly laid on both laboratory and field restoration effects. Moreover, the factors which can affect the stability of cadmium, main interaction mechanisms between nanomaterials and cadmium in the soil, and potential future research direction were also provided. Therefore, it is believed that this work will ultimately contribute to the myriad of environmental cleanup advances, and further improve human health and sustainable development.

Simultaneous immobilization of multi-metals in a field contaminated acidic soil using carboxymethyl-cellulose-bridged nano-chlorapatite and calcium oxide

We prepared and tested carboxymethyl-cellulose-bridged nano-chlorapatite (CMC-CAP) for simultaneous immobilization of Pb, Zn, Cu, and Cd in a field-contaminated acidic soil. Amending the field-contaminated soil using 0.5 wt.% CMC-CAP and 0.1 wt.% CaO was most effective in immobilizing the four metals, which decreased the leachabilities by 98.2%, 98.3%, 96.3%, and 96.2% for Pb, Zn, Cu, and Cd, respectively, after 1 day of treatment. The acid-leached metals fluctuated in the first 60 days, and then approached to steady state after 180 days, where the acid-leachable concentrations all met the regulation levels, and the immobilization was further consolidated when further aged for 365 days. Column elution tests showed that the soil amendment lowered the peak metal concentrations by > 92.5%, and the total eluted masses by >71.9%. Sequential extraction revealed that the soil amendment converted the exchangeable fractions to the much less available Fe-Mn oxides bound and residual forms, and thus, lowered the risk levels to "low risk" for all the metals. The immobilization of the metals was facilitated through formation of stable metal (chloro)phosphates, surface complexation, and/or ion exchange reactions. Combined CMC-CAP and CaO may serve as an effective formulation for simultaneous and long-term immobilization of multiple heavy metals in acidic soil.

In situ prepared algae-supported iron sulfide to remove hexavalent chromium

The effects of algae on the removal of contaminant by iron sulfide (FeS) are still unknown. Chlorella vulgaris (CV), a remarkable algal specie, was used to prepare the CV-supported FeS (CV-FeS) and to investigate the role that CV plays in the removal of a heavy metal (i.e., hexavalent chromium (Cr(VI)) by FeS. The stabilized effect from algal extracellular polymeric substance (EPS) enhanced the reactivity of FeS due to the decrease of FeS aggregation, thus increasing Cr(VI) removal rate from 0.21 min^-1 to 0.79 min^-1. Furthermore, the strong buffering induced by the algal functional groups could effectively prevent the solution pH from increasing, which improved Cr(VI) removal because acidic solution facilitated Cr(VI) reduction by FeS. However, the complexing capacity from algal EPS made Fe(II) unavailable for Cr(VI) reduction, which led to 35% decrease of Cr(VI) removal. The Fe(II) was oxidized to α-FeOOH by Cr(VI) in the absence of CV, while the unreacted Fe(II) was detected as in the form of Fe(OH)₂ in CV-FeS. Cr(VI) was reduced to Cr(III) and S(-II) was oxidized to elemental sulfur (S₈) regardless of the CV. This work showed the different roles of algae in the removal of Cr(VI) by FeS and provided value information for the application of FeS in the polluted algae-containing water system.

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Integrated remediation of sulfate reducing bacteria and nano zero valent iron on cadmium contaminated sediments

Integrated-remediation technologies on heavy metal polluted sediments have received much attention. In this study, Cd contaminated sediments were treated with various conditions: sulfate reducing bacteria (SRB) only and SRB combined with different dosages of nano zero valent iron (nZVI (0.5-10 mg/g)). The immobilization of Cd was found in all remediation treatments according to the decreases of mobile Cd and the increases of more stable Cd compared with control. Five typical SRBs (Desulfobulbaceae, Desulfobacteraceae, Syntrophobacteraceae, Desulfovibrionaceae and Desulfomicrobiaceae) were identified having significant influences on Cd speciation transformation and they could stabilize Cd into sulfide precipitation through dissimilatory sulfate reduction (DSR). The ANOVA results of mobilization index and Cd concentration in overlying water both demonstrated that integrated-remediation systems with 5 mg/g and 10 mg/g of nZVI (Fe5 and Fe10 systems, respectively) presented better immobilization performance than conventional SRB only system (P < 0.05). It is confirmed that nZVI could stimulate the SRB bio-immobilization possibily through providing electrons and enhancing enzyme activities during DSR. The XPS analyses and Pourbaix diagrams revealed that mackinawite may be produced in the Fe10, resulting in the possible formation of Cd-S-Fe. This study indicates that integrated-remediation of SRB and nZVI have great potential in Cd immobilization of sediments, especially with higher addition of nZVI.

Co-existing TiO2 nanoparticles influencing adsorption/ desorption of tetracycline on magnetically modified kaolin

Interaction of coexisting nanoparticles (NPs) and other pollutants may affect their behavior in the environment. In this study, we investigated the effects of TiO₂ NPs on the adsorption and desorption of tetracycline (TC) by magnetized kaolin (MK). The interactions among TC, TiO₂ NPs, and MK were then discussed through their morphology and characteristics by using scanning electron microscopy, X-ray energy dispersive spectrometry, Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Results showed that TiO₂ NPs increased TC adsorption on MK by 2.02% and increased TC desorption by 45.26%, TC increased the maximum adsorption of TiO₂ on MK from 31.32 to 49.42 mg g^-1 and decreased the amount of stable adsorption state TiO₂ NPs on MK from 17.92 to 12.71 mg g^-1. The characterization results demonstrated that TC molecules combined on MK though hydrogen bonding, π-π bonding and hydrophobic interaction. The adsorption of TiO₂ NPs on MK can provide additional hydrogen-bonding sites for TC adsorption by increasing the number of hydroxyl groups. However, TC can decrease the electrostatic attraction sites for TiO₂ NPs adsorption on the MK surface. The complexation of TC and TiO₂ NPs weakened the electrical attraction between MK and TiO₂ NPs and decreased the amount of stable adsorption state TiO₂ NPs.

Effect of multi-walled carbon nanotubes on extractability of Sb and Cd in contaminated soil

The interaction between multi-walled carbon nanotubes (MWCNTs) and soil heavy metals was rarely studied. With the convenience of detecting multiple metal elements by ICP-AES, this paper examined the potential effectiveness of MWCNTs on extractability of antimony (Sb) and cadmium (Cd) in contaminated soil. Three-step sequential extraction procedure, toxicity characteristic leaching procedure, bioaccessibility and CaCl₂ single extraction were employed to evaluate Sb and Cd speciations and their extractabilities. According to our results, only at low Sb content level of 100 mg/kg, antimony bioavailability reduced with MWCNTs addition of 0.3% and 0.9% by 22.97% and 20.74%, respectively, which might due to the increase of adsorption point, nevertheless, the excess Sb(OH)₆^- was not adsorbed more efficiently. Secondly, due to the difference in effective specific surface area, only under the condition of high content level and MWCNTs addition of 0.1%, the mild acid-soluble fraction increased at most by 15.40% for Sb and 9.40% for Cd, respectively. However, in terms of TCLP-extractable Sb and Cd and CaCl₂-extractable Sb and Cd, no significant, continuous, regular extractability pattern were found. Overall, MWCNTs were selective on extractability of soil heavy metals due to mechanisms of physical adsorption. This paper provides data reference for the interaction between MWCNTs and soil heavy metals extractability.