Search Results (9)

The impact of fertilization and irrigation on heavy metal accumulation in saline–alkali soil and its underlying mechanisms are critical issues given the constraints that soil salinization places on agricultural development and crop quality. This study addressed these issues by investigating the effects of adjusting organic fertilizer types, proportions, and irrigation volumes on the physicochemical properties of lightly to moderately saline–alkali soils and analyzing the interaction mechanisms between microorganisms and heavy metals. The results indicate that the rational application of organic fertilizers combined with supplemental irrigation can mitigate soil salinity accumulation and water deficits, and reduce the soil pH, thereby enhancing soil oxidation, promoting nitrogen transformation and increasing nitrate–nitrogen levels. As the proportion of organic fertilizers increased, heavy metal residues, enrichment, and risk indices in the crop grains also increased. Compared to no irrigation, supplemental irrigation of 22 mm during the grain-filling stage increased soil surface Cd content, Zn content, and the potential ecological risk index (HRI) by 10.2%, 3.1%, and 8%, respectively, while simultaneously reducing the heavy metal content in grains by 12–13.5% and decreasing heavy metal enrichment. Principal component analysis revealed the primary factors influencing Cu and Zn residues and Cd accumulation in the crop grains. Soil salinity was significantly negatively correlated with soil pH, organic matter, total nitrogen, and ammonium nitrogen, whereas soil organic matter, total nitrogen, ammonium nitrogen, soil pH, oxidation–reduction potential, soluble nitrogen, and microbial biomass nitrogen were positively correlated. The accumulation and residues of Zn and Cu in the soil were more closely correlated with the soil properties compared to those of Cd. Specifically, Zn accumulation on the soil surface was primarily related to aliphatic organic functional groups, followed by soil salinity. Residual Zn in the crop grains was primarily associated with soil oxidation–reduction properties, followed by soil moisture content. The accumulation of Cu on the soil surface was mainly correlated with the microbial biomass carbon (MBC), whereas the residual Cu in the crop grains was primarily linked to the soil moisture content. These findings provide theoretical insights for improving saline–alkali soils and managing heavy metal contamination, with implications for sustainable agriculture and environmental protection. Full article

The underutilized cement-rich fine fraction of concrete-based demolition waste is a potential sorbent for aqueous metal ion contaminants. In this study, crushed concrete fines (CCF) were found to exclude 33.9 mg g⁻¹ of Cr³⁺, 35.8 mg g⁻¹ of Ni²⁺, and 7.16 mg g⁻¹ of Sr²⁺ from ~1000 ppm single metal nitrate solutions (CCF:solution 25 mg cm⁻³) under static batch conditions at 20 °C after 3 weeks. The removal of Sr²⁺ followed a pseudo-second-order reaction (k₂ = 3.1 × 10⁻⁴ g mg⁻¹ min⁻¹, R² = 0.999), whereas a pseudo-first-order model described the removal of Cr³⁺ (k₁ = 2.3 × 10⁻⁴ min⁻¹, R² = 0.998) and Ni²⁺ (k₁ = 5.7 × 10⁻⁴ min⁻¹, R² = 0.991). In all cases, the principal mechanism of interaction was the alkali-mediated precipitation of solubility-limiting phases on the surface of the CCF. Four consecutive deionized water leaching procedures (CCF:water 0.1 g cm⁻³) liberated 0.53%, 0.88%, and 8.39% of the bound Cr³⁺, Ni²⁺, and Sr²⁺ species, respectively. These findings indicate that CCF are an effective sorbent for the immobilization and retention of aqueous Cr³⁺ and Ni²⁺ ions, although they are comparatively ineffectual in the removal and sustained exclusion of Sr²⁺ ions. As is commonly noted with Portland cement-based sorbents, slow removal kinetics, long equilibrium times, the associated release of Ca²⁺ ions, high pH, and the formation of loose floc may preclude these materials from conventional wastewater treatments. This notwithstanding, they are potentially suitable for incorporation into permeable reactive barriers for the containment of metal species in contaminated groundwaters, sediments, and soils. Full article

This paper presents the synthesis of Fe–Co–Ni nanocomposites by chemical precipitation, followed by a reduction process. It was found that the influence of the chemical composition and reduction temperature greatly alters the phase formation, its structures, particle size distribution, and magnetic properties of Fe–Co–Ni nanocomposites. The initial hydroxides of Fe–Co–Ni combinations were prepared by the co-precipitation method from nitrate precursors and precipitated using alkali. The reduction process was carried out by hydrogen in the temperature range of 300–500 °C under isothermal conditions. The nanocomposites had metallic and intermetallic phases with different lattice parameter values due to the increase in Fe content. In this paper, we showed that the values of the magnetic parameters of nanocomposites can be controlled in the ranges of M_S = 7.6–192.5 Am²/kg, M_r = 0.4–39.7 Am²/kg, M_r/M_s = 0.02–0.32, and H_cM = 4.72–60.68 kA/m by regulating the composition and reduction temperature of the Fe–Co–Ni composites. Due to the reduction process, drastic variations in the magnetic features result from the intermetallic and metallic face formation. The variation in magnetic characteristics is guided by the reduction degree, particle size growth, and crystallinity enhancement. Moreover, the reduction of the surface spins fraction of the nanocomposites under their growth induced an increase in the saturation magnetization. This is the first report where the influence of Fe content on the Fe–Co–Ni ternary system phase content and magnetic properties was evaluated. The Fe–Co–Ni ternary nanocomposites obtained by co-precipitation, followed by the hydrogen reduction led to the formation of better magnetic materials for various magnetically coupled device applications. Full article

Recently, the use of oxide-based nanomaterials for bio-imaging has received great attention owing to their remarkable stabilities as compared to those of conventional organic dyes. Therefore, the development of scalable methods for highly luminescent oxide materials with fine control of size has become crucial. In this study, we suggested modified flame spray pyrolysis (FSP) as a scalable method to produce a green-light emitting phosphor—Tb–doped Y₂O₃—in the nanometer size range. In our FSP method, an alkali salt (NaNO₃) was found to be highly effective as a size-controlling agent when it is simply mixed with other metal nitrate precursors. The FSP of the mixture solution resulted in oxide composites of Y₂O₃:Tb³⁺ and Na_xO. However, the sodium by-product was easily removed by washing with water. This salt-assisted FSP produced nano-sized and well-dispersed Y₂O₃:Tb³⁺ nanoparticles; their crystallinity and luminescence were higher than those of the bulk product made without the addition of the alkali salt. The nanoparticle surface was further coated with silica for biocompatibility and functionalized with amino groups for the attachment of biological molecules. Full article

Present work aimed at evaluating the leaching potential of grape husks biochar, municipal solid wastes compost and their combined application as amendments of sandy Mediterranean soil, in order to assess their capability of releasing/retaining nutrients or heavy metals and therefore their suitability for agricultural applications. Grape husks biochar was produced by pyrolysis at 500 °C in a fixed bed unit. Column leaching experiments, simulating Mediterranean rainfall conditions, were conducted. For all compost/biochar/soil combinations, alkali and alkaline earth metals showed greater solubility, increasing the pH of the extracts and thus decreasing the leachability of heavy metals Cr, Cu, Zr and Sr. Biochar co-application with compost did not prevent the leaching of nitrates, phosphates or trace elements; however, it did lower the chemical oxygen demand and allowed the slower release of sodium, calcium and magnesium from soil. As compared to compost, addition of biochar to soil increased the concentration of potassium by 76%, whereas it decreased that of heavy metals in the leachates by 40%–95%. Grape husks biochar could serve as a better soil amendment than municipal solid wastes compost and if carefully managed could be used as liming agent or fertilizer on acidic soils. Full article

Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst’s properties? Co₄MnAlO_x mixed oxides promoted by potassium calcined at various conditions were tested for direct NO decomposition with the aim to determine their activity, stability and selectivity. The catalysts were prepared by co-precipitation of the corresponding nitrates and subsequently promoted by KNO₃. The catalysts were characterized by atomic absorption spectrometry (AAS)/inductive coupled plasma (ICP), X-ray photoelectron spectrometry (XPS), XRD, N₂ physisorption, temperature programmed desorption of CO₂ (TPD-CO₂), temperature programmed reduction by hydrogen (TPR-H₂), species-resolved thermal alkali desorption (SR-TAD), work function measurement and STEM. The preparation procedure affects physico-chemical properties of the catalysts, especially those that are associated with the potassium promoter presence. The addition of K is essential for catalytic activity, as it substantially affects the catalyst reducibility and basicity—key properties of a deNO catalyst. However, SR-TAD revealed that potassium migration, redistribution and volatilization are strongly dependent on the catalyst calcination temperature—higher calcination temperature leads to potassium stabilization. It also caused the formation of new phases and thus affected the main properties—S_BET, crystallinity and residual potassium amount. Full article

Direct decomposition of nitric oxide (NO) proceeds over Co–Mn–Al mixed oxides promoted by potassium. In this study, answers to the following questions have been searched: Do the properties of the K-promoted Co–Mn–Al catalysts prepared by different methods differ from each other? The K-precipitated Co–Mn–Al oxide catalysts were prepared by the precipitation of metal nitrates with a solution of K₂CO₃/KOH, followed by the washing of the precipitate to different degrees of residual K amounts, and by cthe alcination of the precursors at 500 °C. The properties of the prepared catalysts were compared with those of the best catalyst prepared by the K-impregnation of a wet cake of Co–Mn–Al oxide precursors. The solids were characterized by chemical analysis, DTG, XRD, N₂ physisorption, FTIR, temperature programmed reduction (H₂-TPR), temperature programmed CO₂ desorption (CO₂-TPD), X-ray photoelectron spectrometry (XPS), and the species-resolved thermal alkali desorption method (SR-TAD). The washing of the K-precipitated cake resulted in decreasing the K amount in the solid, which affected the basicity, reducibility, and non-linearly catalytic activity in NO decomposition. The highest activity was found at ca 8 wt.% of K, while that of the best K-impregnated wet cake catalyst was at about 2 wt.% of K. The optimization of the cake washing conditions led to a higher catalytic activity. Full article

The present work highlights the influence of lithology on water quality in Méiganga and its surroundings. The main geological formations in this region include gneiss, granite and amphibolite. The soils developed on these rocks are of ABC type, which are acidic to slightly acidic. Electrical conductivity (EC), organic matter, total nitrogen, nitrate-nitrogen, sulfate, chloride, phosphorus and exchangeable base values were low to very low in the soil samples. Groundwater samples were investigated for their physicochemical characteristics. The wide ranges of EC values (15.1–436 µS/cm) and total dissolved solids (9–249 mg/L) revealed the heterogeneous distribution of hydrochemical processes within the groundwater of the area. The relative abundance of major dissolved species (mg/L) was Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ for cations and HCO₃⁻ >> NO₃⁻ > Cl⁻ > SO₄²⁻ for anions. All the groundwater samples were soft, with total hardness values (2.54–136.65 mg/L) below the maximum permissible limits of the World Health Organization (WHO) guideline. The majority of water samples (67%) were classified as mixed CaMg-HCO₃ type. Alkaline earth metal contents dominated those of alkali metals in 66.66% of samples. Thus, for the studied groundwater, Mg²⁺ and Ca²⁺ ion adsorption by clay minerals was almost nonexistent; this implies their release into the solution, which accounts for their high concentrations compared to alkali metals. Ion geochemistry revealed that water-rock interactions (silicate weathering) and ion exchange processes regulated the groundwater chemistry. One water sample points towards the evaporation domain of this diagram, indicating that groundwater probably does not originate from a deeper system. Kaolinite is the most stable secondary phase in the waters in the study area, in accordance with the geochemical process of monosiallitization, which predominated in the humid tropical zone. Full article

Crystals of congruently melting noncentrosymmetric (NCS) mixed alkali metal nitrate, Rb₂Na(NO₃)₃, have been grown through solid state reactions. The material possesses layers with NaO₈ hexagonal bipyramids and NO₃ triangular units. Rb⁺ cations are residing in the interlayer space. Each NaO₈ hexagonal bipyramid shares its corners and edges with two and three NO₃ units, respectively, in order to fulfill a highly dense stacking in the unit cell. The NaO₈ groups share their six oxygen atoms in equatorial positions with three different NO₃ groups to generate a NaO₆-NO₃ layer with a parallel alignment. The optimized arrangement of the NO₃ groups and their high density in the structure together produce a strong second-harmonic generation (SHG) response. Powder SHG measurements indicate that Rb₂Na(NO₃)₃ has a strong SHG efficiency of five times that of KH₂PO₄ (KDP) and is type I phase-matchable. The calculated average nonlinear optical (NLO) susceptibility of Rb₂Na(NO₃)₃ turns out to be the largest value among the NLO materials composed of only [NO₃]⁻ anion. In addition, Rb₂Na(NO₃)₃ exhibits a wide transparency region ranging from UV to near IR, which suggests that the compound is a promising NLO material. Full article