Nano-hydroxyapatite modified biochar: Insights into the dynamic adsorption and performance of lead (II) removal from aqueous solution.

Adsorption of lead as Pb(II) using biochar is an environmentally sustainable approach to remediate this kind of pollution affecting wastewater. In this study, rice straw biochar (BC) was modified by combination with nano-hydroxy-apatite (HAP), resulting in a material designated as BC@nHAP, with enhanced adsorption performance. Based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, it was evidenced that, after modification, HAP greatly enhanced surface functional groups (i.e., -COOH and/or -OH) of raw biochar's surface. Batch tests showed that the maximum sorption capacity of BC (63.03 mg g-1) was improved due to the modification, reaching 335.88 mg g-1 in BC@nHAP. Pseudo-second order (PSO) kinetics fitted well the adsorption data (R2 = 0.99), as well as the Langmuir isotherm model (showing an adsorption value of 335.88 mg g-1 for qe). The results of thermodynamic calculations showed that the adsorption was primarily governed by chemisorption process. FTIR spectroscopy and XPS spectrum after adsorption further confirmed that the adsorption mechanisms were ion exchange with Pb2+ and surface complexation by -OH and -COOH. In addition, BC@nHAP revealed a brilliant regeneration capability. The maximum adsorption capacity by BC@nHAP was higher than that of raw biochar or other previously reported adsorbents. Therefore, BC@nHAP could be seen as a new sorbent material with high potential for real-scale heavy metal removal from wastewater, and specifically as a capable candidate new sorbent for Pb(II) removal from wastewater, which has clear implications as regard preservation of environmental quality and public health.

Mitigation of greenhouse gas emissions from a red acidic soil by using magnesium-modified wheat straw biochar.

To mitigate greenhouse gas (GHG) emissions, different strategies have been proposed, including application of dolomite, crop straw and biochar, thus contributing to cope with the increasing global warming affecting the planet. In the current study, pristine wheat straw biochar (WBC) and magnesium (MgCl2.6H2O) modified wheat straw biochar (MWBC) were used. Treatments included control (CK), two WBC dosages (1% and 2.5%), and two MWBC doses (1% and 2.5%). After 90 days of incubation, WBC and MWBC improved the soil physiochemical properties, being more pronounced with increasing rates of biochar. MWBC2.5 significantly decreased microbial biomass carbon (MBC), while microbial biomass nitrogen (MBN) increased when both biochar materials (WBC1 and MWBC1) were applied at low rate. Compared to control soil, Urease and Alkaline phosphatase activities increased with the increasing rate of WBC and MWBC. The activities of dehydrogenase and ß-glucosidase decreased with the WBC and MWBC application, compared to CK. The fluxes of all the three GHGs evaluated (CO2, CH4 and N2O) decreased with time for both biochar amendments, while cumulative emission of CO2 increased by 58% and 45% for WBC, and by 54% and 41% for MWBC, as compared to CK. The N2O cumulative emissions decreased by 18 and 34% for WBC, and by 25 and 41% for MWBC, compared to CK, whereas cumulative methane emission showed non-significant differences among all treatments. These findings indicate that Mg-modified wheat straw biochar would be an appropriate management strategy aiding to reduce GHG emissions and improving the physiochemical properties of affected soils, and specifically of the red dry land soil investigated in the current work.

Highly efficient uranium (VI) capture from aqueous solution by means of a hydroxyapatite-biochar nanocomposite: Adsorption behavior and mechanism.

The exploration and rational design of easily separable and highly efficient sorbents with the sufficient capability of retaining radioactive and toxic uranium U(VI) is paramount. In this study, a hydroxyapatite (HAP) biochar nanocomposite (BR/HAP) was successfully fabricated from rice straw biochar (BR), to be used as a new and efficient adsorbent for removing U(VI) from aqueous solution. Both BR and the BR/HAP composite were characterized via Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photo electron spectroscopy (XPS) techniques. Batch test results showed that BR/HAP exhibited remarkably higher adsorption capacity than the raw BR. A pseudo-second order kinetic model thoroughly explained the adsorption kinetics, providing the maximum U(VI) adsorption capacities (qe) of 110.56 mg g-1 (R2 = 0.98) and 428.25 mg g-1 (R2 = 0.99), for BR and BR/HAP, respectively, which was indicative of the rate-limited sorption via diffusion or surface complexation after rapid initial adsorption steps. The Langmuir isotherm model fitted the experimental data to accurately simulate the adsorption of U(VI) onto BR and BR/HAP (R2 = 0.97 and R2 = 0.99). The thermodynamic results showed negative values for ΔG°, clearly indicating that the reaction was spontaneous, as well as positive values for ΔH° (11.04 kJ mol-1 and 28.86 kJ mol-1, respectively) and ΔS° (88.97 kJ mol-1 K-1, and 183.42 kJ mol-1 K-1), making clear the endothermic nature of U(VI) adsorption onto both sorbents, with an increase in randomness at a molecular level. FTIR spectroscopy and XPS spectrum further confirmed that the primary mechanisms were ion exchange with UO22+ and surface complexion by -OH and -COOH. In addition, BR/HAP showed an excellent reusability, making it a promising candidate as a new sorbent for U(VI) removal from wastewater. In view of that, it would be interesting to perform future research to explore practical implications of this sorbent material regarding protection from environmental and public health issues related to that pollutant.

Adsorption of arsenic (III) from aqueous solution by a novel phosphorus-modified biochar obtained from Taraxacum mongolicum Hand-Mazz: Adsorption behavior and mechanistic analysis.

A novel phosphorus (P) modified biochar (PLBC) was produced by pyrolyzing biomass of the dietic herb Taraxacum mongolicum Hand-Mazz (TMHM) and treating it with monopotassium phosphate (KH2PO4). This phosphorous loaded biochar was then assessed as adsorbent for As(III) removal from contaminated water. In the current research, the adsorbent was characterized before and after P loading by means of SEM-EDX, TEM, FTIR and XRD techniques. It was evidenced that the presence of P on the surface of the biochar (BC) could improve its efficiency to remove As(III) from contaminated environments. Adsorption kinetics were evaluated by performing batch-type experiments at varied times and pH values (5, 7 and 9). The kinetic study revealed that a contact time of 24 h was required to attain equilibrium and the experimental data were best fitted to the pseudo-second-order kinetic model (qe = 17.1 mg g-1). In addition, several batch experiments were conducted with varied arsenic concentrations. During the adsorption tests, the maximum adsorption of As(III) was found at pH 5. The adsorption study further showed that compared to BC, PLBC depicted increased removal of As(III) from contaminated solutions. The adsorption experimental data showed the best fit to the Langmuir isotherm model (with R2 = 0.84), with maximum As(III) adsorption capacity reaching 30.76 mg g-1 for PLBC.

Nano-Enable Materials Promoting Sustainability and Resilience in Modern Agriculture.

Intensive conventional agriculture and climate change have induced severe ecological damages and threatened global food security, claiming a reorientation of agricultural management and public policies towards a more sustainable development model. In this context, nanomaterials promise to support this transition by promoting mitigation, enhancing productivity, and reducing contamination. This review gathers recent research innovations on smart nanoformulations and delivery systems improving crop protection and plant nutrition, nanoremediation strategies for contaminated soils, nanosensors for plant health and food quality and safety monitoring, and nanomaterials as smart food-packaging. It also highlights the impact of engineered nanomaterials on soil microbial communities, and potential environmental risks, along with future research directions. Although large-scale production and in-field testing of nano-agrochemicals are still ongoing, the collected information indicates improvements in uptake, use efficiency, targeted delivery of the active ingredients, and reduction of leaching and pollution. Nanoremediation seems to have a low negative impact on microbial communities while promoting biodiversity. Nanosensors enable high-resolution crop monitoring and sustainable management of the resources, while nano-packaging confers catalytic, antimicrobial, and barrier properties, preserving food safety and preventing food waste. Though, the application of nanomaterials to the agri-food sector requires a specific risk assessment supporting proper regulations and public acceptance.

Fabrication, characterization and U(VI) sorption properties of a novel biochar derived from Tribulus terrestris via two different approaches.

Water contamination due to radionuclides is considered a crucial environmental issue. In this study, Tribulus terrestris plant biomass was used as a precursor for obtaining biochar (BC), that was further modified by two different methods using FeCl3 to obtain two different magnetic biochars. Both (one-step biochar, called 1S-BC, and two-steps biochar, called 2S-BC) were studied to investigate their capability for adsorbing/removing uranium (VI) from aqueous solutions. The U(VI) removal efficacy of both biochars was tested for different values of pH, ionic strength, initial concentration of U(VI) and temperature. Experimental adsorption data fitted well to the Freundlich model (achieving as highest value for adsorption capacity KF = 49.56 mg g-1 (mg L-1)-1/n, R2 = 0.99). Thermodynamic studies revealed that adsorption was endothermic, characterized by inner-sphere complexation, and entropy-driven with a relatively increased randomness in the solid-solution interface. X-ray photoelectron spectroscopy (XPS) revealed that U(VI) sorption took place by surface complexation between U(VI) and oxygen containing functional groups on both biochars. Five consecutive regeneration cycles verified an excellent reusability for 1S-BC. The overall results allow to conclude that the FeCl3 modification of the biochar obtained from Tribulus terrestris plant biomass could give an efficient alternative adsorbent for U(VI) removal in a variety of environmental conditions, promoting protection of the environment and human health, as well as facilitating resource utilization and sustainable management of the materials studied.

Enhanced adsorption of aqueous Pb(II) by modified biochar produced through pyrolysis of watermelon seeds.

A biochar (BC) was obtained by the pyrolysis of watermelon seeds (WM) in nitrogen environment. In addition, a modified biochar (HP-BC) was obtained by means of H2O2 treatment of BC. Later on, both kinds of biochar (BC and HP-BC) were characterized and compared as regards their potential for Pb(II) adsorption from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Pb(II) adsorption characteristics for HP-BC and BC as were evaluated as a function of solution pH, contact time and Pb(II) equilibrium concentration, using kinetic and thermodynamic studies, as well as adsorption isotherms. Regarding kinetics, the pseudo-second order model showed good fitting to experimental data. Based on the Langmuir model, the maximum Pb(II) adsorption capacities were calculated as 44.32 mg g-1 and 60.87 mg g-1 for BC and HP-BC, respectively. Thermodynamic study indicated that Pb(II) adsorption onto BC and HP-BC was spontaneous and primarily governed by chemisorption and surface complexation. In view of the results, the H2O2 modification of the watermelon seeds biochar can be considered as a promising and cost effective approach as regards Pb(II) removal from water/wastewater, which would not cause adverse impacts on the surrounding environments. Overall, it can be seen as a procedure promoting the effective recycling of a waste/by-product, in line of the precepts of the circular economy, aiding to protect human and environmental health.

Utilization of Citrullus lanatus L. seeds to synthesize a novel MnFe2O4-biochar adsorbent for the removal of U(VI) from wastewater: Insights and comparison between modified and raw biochar.

Uranium (U) is a radioactive and highly toxic metal. Its excessive concentrations in the aqueous environments may result in severe and irreversible damage. To fight this hazard, a raw biochar was prepared from Citrullus lanatus L. seeds, then characterized and compared with a MnFe2O4 modified biochar, both tested for U(VI) adsorption from wastewater, which was assayed for the first time in this study. The characterization of the adsorbent materials was performed by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) with elemental mapping, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) techniques. The effects of solution pH, concentration of sorbate and sorbents, temperature, time and ionic strength were assessed as regards their influence on U(VI) adsorption. The experimental adsorption data showed good fit to a pseudo-second-order kinetic model (reaching a value of qe = 15.12 mg g-1, R2 = 0.96 at equilibrium), and to the Langmuir isotherm (achieving a maximum score of qmax = 27.61 mg g-1, R2 = 0.96). The maximum adsorption capacity was found at 318 K. The results of the study indicate that the binding of negatively charged functional groups (carbonyls, hydroxyls, and some carboxylic groups) with MnFe2O4 significantly enhanced U(VI) adsorption. In view of the overall results, it can be concluded that the MnFe2O4 modification of the Citrullus lanatus L. seeds biochar could give an efficient alternative adsorbent for U(VI) removal in a variety of environmental conditions, simultaneously promoting resource utilization and good sustainable management of the materials studied, aiding to protect the environment and human health.

Impacts of long-term inorganic and organic fertilization on phosphorus adsorption and desorption characteristics in red paddies in southern China.

Soil phosphorus (P) adsorption and desorption occur in an important endogenous cycle linked with soil fertility problems and relevant to the environmental risk assessment of P. In our study, the effect of long-term inorganic and organic fertilization on P adsorption and desorption characteristics in relation to changes in soil properties was evaluated by selecting three long-term experimental sites in southern China. The selected treatments at each site were CK (unfertilized), NPK (synthetic nitrogen, phosphorus and potassium) and NPKM (synthetic NPK plus manure). The adsorption and desorption characteristics of P were evaluated using Langmuir and Freundlich isotherms. The results showed that long-term application of NPK plus manure significantly increased soil organic carbon (SOC), total P and available P at all three sites compared with the NPK and CK treatments. All three treatments fit these equations well. The maximum adsorption capacity (Qm) of P increased with NPKM treatment, and the binding energy of P (K) and the maximum buffering capacity (MBC) showed increasing trends. NPKM showed the highest Qm (2346.13 mg kg-1) at the Jinxian site, followed by Nanchang (221.16 mg kg-1) and Ningxiang (2219.36 mg kg-1). Compared to CK and NPK, the NPKM treatment showed a higher MBC as 66.64, 46.93 and 44.39 L kg-1 at all three sites. The maximum desorption capacity (Dm) of P in soil was highest with the NPKM treatment (157.58, 166.76, 143.13 mg kg-1), showing a better ability to release P in soil. The correlation matrix showed a significant positive correlation of SOC, total and available P with Qm, Dm and MBC. In conclusion, it is suggested that manure addition is crucial to improve P utilization in red paddy soils within the recommended range to avoid the risk of environmental pollution.

The sorbed mechanisms of engineering magnetic biochar composites on arsenic in aqueous solution.

The aim of this study was to produce magnetic biochar for the removal of As (III) from the aquatic environment. Magnetic biochar (MBC) was prepared from corn straw­derived biochar. Pristine biochar (BC) was impregnated with iron oxide and relative analyses were performed on the adsorption capacity of BC's and MBC's. After impregnation, the specific surface area of MBC800-0.6300 increased from 79.66 to 309.7 m2 g-1 and superparamagnetic magnetization was about 9.75 emu g-1 contributed by the contained Fe3O4. Results of MBC800-0.6300 showed maximum adsorption capacity (Qmax) 22.94 mg g-1 for As (III) based on Langmuir model which is 5.71 times higher than the adsorption capacity of BC800 (4.02 mg g-1). The adsorption of As (III) increased significantly due to the successful loading of iron oxide and the increased oxygen functional groups that were confirmed by XPS and FTIR results. The removal of As (III) followed Langmuir isotherm model and pseudo-second-order (R2 ≥ 0.99), indicated that the adsorption rate was monolayer and depended on the chemical adsorption process, respectively. Consequently, the simple preparation procedure and high adsorption performance suggest that MBC800-0.6300 could be used as an environment-friendly and extremely effective adsorbent for As (III) removal from aqueous environment.

Interaction of liming and long-term fertilization increased crop yield and phosphorus use efficiency (PUE) through mediating exchangeable cations in acidic soil under wheat-maize cropping system.

Low phosphorus use efficiency (PUE) is one of the main problems of acidic soil that limit the crop growth. Therefore, in the present study, we investigated the response of crop yield and PUE to the long-term application of fertilizers and quicklime (CaO) in the acidic soil under wheat-maize rotation system. Treatments included, CK (no fertilization), NP (inorganic nitrogen and P fertilization), NPK (inorganic N, P and potassium fertilization), NPKS (NPK + straw return), NPCa (NP + lime), NPKCa (NPK + lime) and NPKSCa (NPKS + lime). Results showed that, fertilizer without lime treatments, significantly (p ≤ 0.05) decreased soil pH and crop yield, compared to the fertilizer with lime treatments during the period of 2012-2018. Average among years, compared to the CK treatment, wheat grain yield increased by 138%, 213%, 198%, 547%, 688% and 626%, respectively and maize yield increased by 687%, 1887%, 1651%, 2605%, 5047% and 5077%, respectively, under the NP, NPK, NPKS, NPCa, NPKCa and NPKSCa treatments. Lime application significantly increased soil exchangeable base cations (Ca2+ and Mg2+) and decreased Al3+ cation. Compared to the NP treatment, phosphorus use efficiency (PUE) increased by 220%, 212%, 409%, 807% and 795%, respectively, under the NPK, NPKS, NPCa, NPKCa and NPKSCa treatments. Soil pH showed significant negative relationship with exchangeable Al3+ and soil total N. While, soil pH showed significant (p ≤ 0.05) positive relationship with exchangeable Ca2+, PUE and annual crop yield. PUE was highly negatively correlated with soil exchangeable Al3+. In addition, soil exchangeable Ca2+, pH, exchangeable Al3+ and available N were the most influencing factors of crop yield. Therefore, we concluded that lime application is an effective strategy to mitigate soil acidification and to increase PUE through increasing exchangeable base cations and reducing the acidic cations for high crop yield in acidic soil.

Soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry drives phosphorus lability in paddy soil under long-term fertilization: A fractionation and path analysis study.

Soil C:N:P stoichiometry plays a vital role in nutrient cycling in ecosystems, but its importance to P transformation in paddy soil remains unclear. We investigated the effect of soil C:N:P stoichiometry on P mobility and uptake under long-term fertilization. Three treatments, CK (no fertilization), NPK (inorganic nitrogen, phosphorus and potassium fertilization) and NPKM (combined inorganic NPK fertilizer and manure application), were selected from two long-term experiments of paddy soil that were initiated in 1991 and 1982 in Chongqing and Suining, respectively. The results showed that in comparison the control treatment, under long-term fertilization, soil pH decreased. In comparison with the NPK and CK treatments, the NPKM treatment significantly increased soil nutrient contents, P uptake and phosphatase activities. In comparison to the CK treatment, the NPK and NPKM treatments significantly decreased soil C:N, C:P and N:P ratios. In comparison to NPK and CK treatments, the NPKM treatment decreased residual-P at both sites. Compared with CK treatment, the NPKM treatments increased labile-P and moderately labile-P by 987% and 144%, respectively, and NPK treatment increased these factors by 823% and 125%, respectively, at the Chongqing site. At the Suining site, with NPKM treatment, increases in labile-P and moderately labile-P were 706% and 73%, respectively, and with NPK treatment, the increases were 529% and 47%, respectively. In contrast, non-labile-P was significantly decreased with NPKM treatment in comparison to that with NPK and CK treatments. Moreover, increases in soil C:N and C:P ratios decreased the labile-P pools and increased non-labile-P pools. A path analysis indicated that soil C:N:P stoichiometry indirectly controlled P uptake by directly affecting P transformation from non-labile to labile-P pools. Moreover, the non-labile-P in soil with high SOM and P content directly affected P uptake, indicating that soil P transformation is mainly driven by soil C and P in paddy soil. In conclusion, understanding mechanism of P mobility influenced by soil C:N:P stoichiometry could be helpful to manage soil P fertility under long-term fertilization in paddy soils of these regions.

Changes in phosphorus fractions associated with soil chemical properties under long-term organic and inorganic fertilization in paddy soils of southern China.

The identification of phosphorus (P) fractions is essential for understanding the transformation and availability of P in paddy soils. To investigate the soil P fractions associated with soil properties under long-term fertilization, we selected three fertilization treatments, including no fertilization (CK), chemical fertilizers (NPK) and chemical fertilizers combined with manure (NPKM), from three long-term experiments located in Nanchang (NC), Jinxian (JX) and Ningxiang (NX). The results showed that chemical fertilizers combined with manure (NPKM) significantly (P ≤ 0.05) increased the soil total phosphorus, Olsen P and soil organic matter (SOM) by 2, 3 and 1 times, respectively, compared with the NPK treatment, and by 4, 17 and 2 times, respectively, compared with the CK treatment. NPKM significantly increased the grain yield compared with CK and NPK at all sites. The apparent P balance with NPK was higher in NC and NX but lower in JX compared with NPKM. Hedley fractionation revealed the predominance of most of the organic and inorganic phosphorus (Po and Pi) fractions with long-term fertilization, especially with the NPKM treatment, at all sites. The nonlabile P pool decreased by 14% and 18% whereas the moderately labile P pool proportions increased by 3 and 6 times with the NPK and NPKM treatments, respectively, compared to the CK treatment. The labile P pool showed a significant positive relationship with the SOM, total P and Olsen P contents. The moderately labile P was positively correlated with the total P and Olsen P. A significant positive correlation was observed between soil pH and the nonlabile P pool. Redundancy analysis revealed that the moderately labile P fraction (HCl dil. Pi fraction) was remarkably increased by the NPKM treatment and significantly correlated with the soil pH and total P concentration. The labile P fraction (NaHCO3-Pi) showed a strong relationship with the Olsen P and total P. However, the residual P fraction was negatively correlated with the HCl. dil. Pi fraction. We concluded that NPKM application improved P availability by many folds compared to NPK, which could lead to environmental pollution; therefore, the rate of combined application of manure and chemical fertilizer should be reduced compared to chemical fertilizer inputs to minimize the wastage of resources and environmental P losses.

Zinc fertilisation increases grain zinc and reduces grain lead and cadmium concentrations more in zinc-biofortified than standard wheat cultivar.

Given that plant uptake and transport systems for metals have some similarities, zinc (Zn)-biofortified cultivars may concurrently accumulate non-essential toxic heavy metals in grains. However, Zn-biofortified cultivars have never been tested for heavy metal accumulation in grains. In a pot experiment, we compared Zn-biofortified wheat (Zincol-2016) with a standard wheat (Faisalabad-2008) cultivar on heavy-metal-contaminated soils for yield response and grain accumulation of Zn, lead (Pb) and cadmium (Cd), without or with Zn fertilisation (8mgZnkg-1). The soils, collected from agricultural fields in (i) industrial zone and (ii) peri-urban area, had been receiving industrial and city effluents for >20years. In the two soils, Zn fertilisation significantly (P≤0.05) increased grain yield of both cultivars. Zinc fertilisation increased grain Zn concentration of Zincol-2016 and Faisalabad-2008 by respectively 32 and 18% in industrial-zone soil, and by 15 and 2% in peri-urban soil. Averaged across Zn rates, Zincol-2016 accumulated in grains more than double the Zn amount than Faisalabad-2008 in industrial-zone soil. At 0mgZnkg-1, grain Pb and Cd concentrations were respectively 26 and 33% greater in Zincol-2016 than Faisalabad-2008 in industrial-zone soil, and 86 and 50% greater in Zincol-2016 than Faisalabad-2008 in peri-urban soil. Zinc fertilisation significantly (P≤0.05) decreased concentration of Pb and Cd in grains of both cultivars. In industrial-zone soil, a toxic level of Pb in grains (0.24mgkg-1) was attained at control rate of Zn by Zincol-2016, and was decreased to a safe level (0.07mgkg-1) by application of 8mgZnkg-1. Therefore, biofortified cultivars should not be grown in contaminated soils, and/or sufficient Zn must be applied, to decrease accumulation of non-essential toxic heavy metals in grains. Moreover, future breeding efforts should be directed toward selection of biofortified cultivars that would selectively accumulate Zn in grains, but not the contaminants.