Copper-contained products that are widely employed yearly in viticulture for vine disease management, lead to Cu accumulation in topsoil creating an increased risk for land workers and for leaching and/or uptake of Cu by plants, especially in acidic soils where Cu mobility is higher. In this study, the impact of two biochar types on Cu distribution and redistribution in fractions was evaluated in four acidic vineyard soils in relation to incubation time. The two biochars were derived from sewage sludge (SG) and olive tree prunings (OL). Soils (control) and biochar-amended soils with application rate of 20 % (w/w) were spiked with CuCl₂ (160 mg kg⁻¹) and incubated in the laboratory at ambient temperature 22 ± 5 °C. After 1, 3, 7, 15, 36, and 90 days of incubation, modified BCR sequential extraction procedure was used to determine Cu distribution in the four soil chemical phases and to examine potential Cu redistribution between these fractions both in soils and in amended soils with biochars. Results show that biochar amendment affects Cu distribution in different soil fractions. In SG treatment, from the 1st and up to 36th incubation day, both exchangeable and reducible Cu fractions decreased, while oxidizable Cu increased, in relation to control soils. At 90th incubation day, a redistribution of Cu was observed, mainly from the oxidizable to the residual fraction. In OL treatment, during the first 36 incubation days exchangeable and oxidizable Cu slightly increased, while reducible Cu decreased. At the 90th incubation day the higher percentage of Cu was extracted from the residual fraction, but exchangeable Cu was present in remarkable quantities in the three of the four studies soils. SG application in the studied soils highly restricted the availability of added Cu promoting Cu-stable forms thus reducing the environmental risk while OL did not substantially reduce Cu available fraction over the experimental incubation period. Fourier transformation infrared analysis (FTIR) provided convincing explanations for the different behavior of the two biochar types.

To better understand the amendment effects and mechanisms of aluminum (Al(III)) phytotoxicity mitigation by different regional crop straw biochars, wheat seedling root elongation trials were conducted. The contributions of liming effect, oxygen-containing surface functional group adsorption, and oxyanions precipitation to Al(III) phytotoxicity mitigation by Ca(OH)₂, pristine and ash-free canola straw biochar were evaluated. The results indicated that biochars derived from canola straw collected from four different regions (Yingtan, Xuancheng, Nanjing, and Huaiyin) caused 22–70% wheat seedling root elongation, which might be linked to liming effect. Incorporation of the corresponding ash-free biochars caused 15–30% elongation, which could be attributed to the surface functional group adsorption. About 0–60% of changes could be explained by Al(III) precipitation with inorganic oxyanions. These findings provide new insights into the physicochemical properties, potential applications, efficiencies, and underlying mechanisms of crop straw biochar in alleviating Al(III) phytotoxicity, which is dependent on the cultivation soil, and indicate similar application of crop straw biochar for acidic soil amelioration, contaminated soil remediation, and arable soil improvement. Graphical Abstract

Biochar derived from biomass is regarded as a promising adsorbent for wastewater treatment, but the high cost of modification is still a challenge for its large-scale practical applications. In this study, we employed steel slag as a low-cost fabricant and synthesized hydrothermally carbonized steel slag (HCSS), as a stable environmentally functional material for heavy metal removal. Typically, positively and negatively charged heavy metal contaminants of Hg²⁺ and Cr₂O₇²⁻ were employed to testify the performance of HCSS as an adsorbent, and good capacities [(283.24 mg/g for Hg (II) and 323.16 mg/g for Cr (VI)] were found. The feasibility of HCSS on real wastewater purification was also evaluated, as the removal efficiency was 94.11% and 88.65% for Hg (II) and Cr (VI), respectively. Mechanism studies revealed that the modification of steel slag on bio-adsorbents offered copious active sites for pollutants. As expected, oxygen-containing functional groups in HCSS acted as the main contributor to adsorption capacity. Moreover, some reactive iron species (i.e., Fe²⁺) played an essential role in chemical reduction of Cr (VI). The adsorptive reactions were pH-dependent, owing to other more mechanisms, such as coprecipitation, ion-exchange, and electrostatic attraction. This promising recycling approach of biomass waste and the design of agro-industrial byproducts can be highly suggestive of the issues of resource recovery in the application of solid waste-derived environmentally functional materials for heavy metal remediation.

Sensitive detection and efficient removal of heavy metal ions with high toxicity and mobility are of great importance for environmental monitoring and control. Although several kinds of functional materials have been reported for this purpose, their preparation processes are complicated. Herein, nitrogen self-doped activated porous biochar (NAC) was synthesized in a facile process via an activation–carbonization strategy from cicada shell rich in chitin, and subsequently employed as an effective functional material for the simultaneous determination and removal of Cu²⁺ from aqueous media. With its unique porous structure and abundant oxygen-containing functional groups, along with the presence of heteroatoms, NAC exhibits high sensitivity for the electrochemical sensing of Cu²⁺ in concentrations ranging from 0.001 to 1000 μg·L⁻¹, with a low detection limit of 0.3 ng·L⁻¹. Additionally, NAC presents an excellent removal efficiency of over 78%. The maximum adsorption capacity is estimated at 110.4 mg/g. These excellent performances demonstrate that NAC could serve as an efficient platform for the detection and removal of Cu²⁺ in real environmental areas.

Heavy metals including Cd, Pb, and Zn are prevalent stormwater and groundwater contaminants derived from natural and human activities, and there is a lack of cost-effective treatment for their removal. Recently, biochar has been increasingly recognized as a promising low-cost sorbent that can be used to remediate heavy metal contaminated water. This study evaluates the immobilization/release performance of dairy manure-derived biochar (DM-BC) as a sustainable material for competitive removal of coexisting heavy metal ions from water and explains the underlying mechanism for regeneration/reusability of biochar. Results showed that the metal ions exhibited competitive removal in the order of ${\mathrm{Pb}}^{2+}\gg {\mathrm{Zn}}^{2+}>{\mathrm{Cd}}^{2+}$ . The pH played a decisive role in influencing metal ion speciation affecting the electrostatic attraction/repulsion and surface complexation. Higher pH led to greater removal for ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ , whereas ${\mathrm{Zn}}^{2+}$ showed maximum removal at $\mathrm{pH}\approx 7.5$ . Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and X-ray diffraction confirmed the interactions and precipitation reactions of oxygen-containing functional groups (e.g., ─ OH, ${\mathrm{CO}}_3^{2-}$ , and Si─ O) as key participants in metal immobilization. Langmuir, Freundlich, and Redlich–Peterson isotherm modeling data showed varied and unique results depending on the metal ion and concentration. The removal kinetics and model fitting showed that the three steps of intraparticle diffusion might be more representative for describing the immobilization processes of metal ions on the external surface and internal pores. In the flow-through columns, DM-BC effectively retained the mixed metal ions of ${\mathrm{Cd}}^{2+}$ , ${\mathrm{Pb}}^{2+}$ , and ${\mathrm{Zn}}^{2+}$ showing 100% removal for the duration of the column run over three cycles of regeneration and reuse.

In this paper, the material types were preferentially selected for different kinds of heavy metals, the effect of calcination temperatures on metal adsorption was investigated, and the adsorption mechanism was explored and summarized. The results show that the pseudo-first-order kinetic was better to fit the adsorption of heavy metals. The biomass type and pyrolysis temperature had an effect on the rate at which heavy metals were absorbed. Based on their adsorbed capacity, 350 °C pyrolyzed corn stalk char, 550 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, and 500 °C pyrolyzed wheat stalk char were shown to be the best adsorbents for , Cd2+, Cu2+, Zn2+ and Pb2+, respectively. The largest adsorption rate were in the order of Cr6+ (, 0.5380 /min) > Pb2+ (0.2276 /min) > Cd2+ (0.1354 /min) > Cu2+ (0.1273 /min) > Zn2+ (0.1000 /min), which might be positively related to the ion radius. Meanwhile, the yield of biomass decreased from 43.9% to 29.0% with the increase of pyrolysis temperature from 350 °C to 550 °C. In addition, the specific surface area and functional groups of the biochar, as well as the ionic radius and initial concentration of heavy metals affect the adsorption rate.

A simply synthetic ferrihydrite-modified biochar ([email protected]) was applied to simultaneously remove As(III) and Cd(II) from the aqueous solution, and then to explore the mutual effects between As(III) and Cd(II) and the corresponding mechanisms. The Langmuir maximum adsorption capacities of As(III) and Cd(II) in the single adsorbate solution were 18.38 and 18.18 mg g⁻¹, respectively. It demonstrated that [email protected] was a potential absorbent material for simultaneous removal of As(III) and Cd(II) in aqueous solution. According to the XRF, SEM–EDS, FTIR, XRD, and XPS analysis, the mechanisms of simultaneous removal of As(III) and Cd(II) by [email protected] could be attributable to the cation exchange, complexation with R-OH and Fe-OH, and oxidation. Moreover, the mutual effect experiment indicated that Cd(II) and As(III) adsorption on [email protected] in the binary solution exhibited competition, facilitation and synergy, depending on their ratios and added sequences. The mechanisms of facilitation and synergy between Cd(II) and As(III) might include the electrostatic interaction and the formation of both type A or type B ternary surface complexes on the [email protected]

In this study, dithiocarbamate functionalized activated carbon (DTC-AC) was synthesized with nitric acid, tetraethylenepentamine (TEPA), and carbon disulfide (CS₂). N₂ adsorption–desorption technology, SEM, FTIR, and elemental analysis demonstrated the successful preparation of adsorption materials. Batch adsorption experiments were conducted to evaluate the influence of variable conditions on the adsorption behavior of Pb(II), Cu(II), and Cd(II) onto DTC-AC. Experimental data were fitted with adsorption kinetics models and isothermal models. The findings confirmed that DTC-AC exhibited a superior heavy metal adsorption capacity to oxidized AC (O-AC) and AC, and that pH played an important role in heavy metal removal by altering the surface charge. The adsorption kinetics study showed that the adsorption equilibrium was attained within 20 min, and the adsorption rate was dependent on both physisorption and chemisorption. The Langmuir model best described the adsorption performance of DTC-AC, and the maximal single metal uptake for Pb(II), Cu(II), and Cd(II) was 203.36, 53.13, and 102.89 mg g⁻¹, respectively. Moreover, DTC-AC showed selective adsorption for Pb(II) in the ternary metal species system. Additionally, thermodynamic parameters showed that the adsorption process of heavy metals onto DTC-AC was spontaneous and endothermic. The heavy metal removal efficiency of DTC-AC remained above 85% after five consecutive adsorption–desorption cycles. This study showed that DTC-AC is an effective and reusable adsorbent with great potential for application in remediating heavy metal pollution.

In this paper, amino modified silica fiber cloth (KSF) was prepared by the chemical grafting method. The SEM, FTIR and TGA techniques were employed for the characterization of the silica fiber cloth (SF) and KSF. FTIR analysis suggests that functional amino groups of γ-aminopropyl triethoxysilane (KH550) were grafted on the surface of KSF. The influence of single factor on adsorption performance was studied. The results showed that the adsorption capacity of KSF can reach 178.46 mg-g¹, the experimental adsorption data were fitted closely by pseudo-second-order kinetic model, adsorption isotherms were simulated well by Langmuir model. Thermodynamic analysis revealed that the adsorption process was endothermic, entropy-driven and spontaneous. The adsorption-desorption experiments demonstrated that KSF showed no significant removal efficiency loss even after ten consecutive cycles, indicating the good stability of prepared KSF material. Our findings suggested the KSF can serve as potential candidates for the practical application of wastewater containing heavy metals.