Search Results (1,114)

Olive pomace (OP), an abundant byproduct of the olive oil industry, was investigated as a low-cost precursor for the production of hydrochar-based adsorbents for methylene blue (MB) removal from water. Hydrothermal carbonization (HTC) was performed at 180 and 220 °C with different residence times, followed by soft alkaline activation (SAA), consisting of alkaline treatment and carbonization at 300 °C, and post-washing to improve the adsorption performance. The materials were characterized by ATR-FTIR, Raman spectroscopy, XRD, SEM-EDX, BET, and mercury intrusion porosimetry. HTC increased the degree of carbonization and surface area, but non-activated hydrochars showed lower adsorption capacity than untreated OP because of the loss of oxygenated functional groups. Among non-activated hydrochars, OP_220_1 showed the highest adsorption capacity (20.7 mg g⁻¹). SAA increased the adsorption capacity of the hydrochar by 63%, while washing further enhanced performance by removing carbonate precipitates and restoring pore accessibility. The washed activated hydrochar derived from OP_220_1 achieved the highest adsorption capacity (69.9 mg g⁻¹ at 250 mg L⁻¹ MB) and BET surface area (40.0 m² g⁻¹). Kinetics followed the pseudo-second-order model, while washing shifted the isotherm behavior from Langmuir to Freundlich. A performance-based assessment showed that the washed activated hydrochar reduced adsorbent demand by 49% compared with untreated OP. Full article

Lead (Pb²⁺) pollution poses a severe threat to the ecological environment and human health due to its high toxicity, bioaccumulation, and refractory nature. Traditional treatment technologies for lead-contaminated wastewater, such as chemical precipitation, ion exchange, and membrane separation, often face limitations, including secondary pollution, high costs, and high energy consumption. In contrast, adsorption has emerged as a promising alternative technology with advantages such as a simple process, high efficiency at low concentrations, and renewability. Biomass-based hydrogels and their composite systems, as novel green adsorbent materials, combine the abundant functional groups of natural biomass with the structural stability, high porosity, and recoverability of hydrogels through a three-dimensional cross-linked network, offering unique advantages for lead ion adsorption. Depending on their composition, these systems range from fully biodegradable pure biopolymer networks to partly biodegradable or biomass-containing composites incorporating inorganic, carbon-based, or metal–organic framework (MOF) materials. This paper systematically reviews the latest research progress on cellulose, lignin, sodium alginate, chitosan, starch-based hydrogels, and their composite systems for lead (Pb²⁺) adsorption. First, the structural characteristics, cross-linking mechanisms, and functional modification strategies of various biomass hydrogels are introduced. Then, the adsorption mechanisms of Pb²⁺, including multiple modes of action such as coordination complexation, ion exchange, electrostatic interaction, and physical adsorption, are systematically analyzed. The adsorption performance of different material systems is compared in detail. The regeneration and recycling performance, as well as the potential practical applications, of the materials are evaluated. On this basis, the main challenges in current research are summarised: balancing adsorption capacity and mechanical strength, achieving selective adsorption in actual wastewater, improving regeneration efficiency, and optimizing costs. In addition, future development directions for biomass hydrogel adsorbent materials are discussed, including the design of multi-functional composite materials, the development of intelligent, responsive hydrogels, engineering-scale-up, and life-cycle assessment. This review aims to provide a theoretical framework and technical roadmap for the rational design of high-performance, sustainable hydrogel adsorbents and to promote their engineering application for the treatment of lead-contaminated wastewater. Full article

Tannin-modified Li₂TiO₃ powders (TA-Li₂TiO₃) were prepared by a precipitation-peptization process with titanium sulfate as the titanium source, lithium acetate as the lithium source, ammonia as the precipitator, and hydrogen peroxide as the complexing agent. The effects of the tannin addition ratio and the calcination temperature on the crystal structure and surface morphology of TA-Li₂TiO₃ were studied. After pickling TA-Li₂TiO₃ with diluted hydrochloric acid, TA-H₂TiO₃ was obtained. Its elution behavior and lithium adsorption performance were studied and the adsorption isotherm and kinetics were investigated. The results indicated that the crystal structure was well-defined, and a uniform mesoporous surface morphology was observed on the sample surface with a calcination temperature of 750 °C and a tannin addition ratio of 1 g:1 L. The specific surface area was increased by 15.1 m²/g compared with the unmodified one, and the hydrophilicity of the TA-H₂TiO₃ significantly improved. After elution with 0.2 mol/L hydrochloric acid for 8 h, the elution equilibrium was achieved, the lithium elution ratio reached 98.15% and the lithium adsorption capacity reached 39.13 mg/g, which were significantly higher than that of the unmodified one. The adsorption isotherm is more consistent with the Langmuir model, the adsorption kinetics follows the pseudo second order model, and the adsorption mechanism is chemical monolayer adsorption. Full article

Dye wastewater pollution has become a critical environmental issue, while conventional silica adsorbents are often limited by high production costs and the use of chemical silicon sources. In this study, a black-liquor-derived silica-based adsorbent was prepared from bamboo alkaline black liquor through calcium hydroxide precipitation, acid leaching, washing, and calcination. The obtained product was systematically characterized by ICP-OES, XRD, SEM, and BET analysis. Phase analysis showed that the product was mainly composed of amorphous SiO₂, together with a small amount of residual CaSiO₃. The product was semi-quantitatively estimated to contain approximately 64.6 wt.% total SiO₂ and 14.7 wt.% total CaSiO₃, and the estimated SiO₂ yield was about 4.6 wt.% based on dry black liquor solids. The adsorbent exhibited a mesoporous structure with a specific surface area of 60.04 m²/g, a pore volume of 0.23 cm³/g, and an average pore diameter of 7.5 nm. The effects of adsorbent dosage, initial methylene blue concentration, solution pH, and temperature on adsorption performance were investigated. Under the selected conditions of 0.5 g adsorbent, 50 mg/L methylene blue, pH 7, and 20 °C, the removal efficiency reached 82.94%. Adsorption isotherm analysis showed that the Langmuir equation provided the best fit among the tested models over the studied concentration range, and the linear Langmuir fit gave an apparent capacity parameter of 840.3 mg/g. However, this fitted value should not be interpreted as a physically realizable ideal monolayer uptake. This work provides a feasible route for converting silicon-containing bamboo alkaline black liquor into a mesoporous silica-based adsorbent for dye removal. Full article

At low temperatures, the preferential removal of CO from the fuel feed of PEMFC is a critical factor for ensuring the optimal performance of fuel cells. In this study, Au/TiO₂-PD and Au/TiO₂-DP catalysts were synthesized via in situ photo-deposition and deposition–precipitation methods, respectively. The catalytic performance for CO preferential oxidation was evaluated in a hydrogen-rich atmosphere, and the effects of visible light irradiation on catalytic activity and selectivity were systematically investigated. The Au/TiO₂-DP catalyst exhibited a relatively low CO conversion under dark conditions in the hydrogen-rich atmosphere, while visible light irradiation significantly enhanced its CO oxidation activity and selectivity. In contrast, the Au/TiO₂-PD catalyst achieved a high CO oxidation conversion, but suffered from low CO oxidation selectivity; moreover, visible light exerted a weak inhibitory effect on its selectivity. Combined characterization results from temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR), in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and in situ electron paramagnetic resonance (EPR) revealed that the Au/TiO₂-PD catalyst possessed stronger hydrogen adsorption, dissociation and oxidation capabilities than the Au/TiO₂-DP catalyst. The rapid dissociation of hydrogen molecules over the Au/TiO₂-PD catalyst accelerated the activation of adsorbed oxygen species and simultaneously promoted the formation of water via hydrogen oxidation. Excessive water accumulation on the catalyst surface occupied the active sites for CO oxidation, thereby imposing an overall inhibitory effect on CO preferential oxidation. Full article

This study was conducted to determine the optimal mineralization enhancement period for recycled aggregates, and to elucidate the mechanisms underlying the mineralization enhancement of recycled aggregates and the self-healing of concrete cracks. Microbial-induced calcium carbonate precipitation enables the self-healing of concrete cracks: microbial carriers can effectively increase the survival rate of microorganisms within the concrete matrix, thereby enhancing the self-healing performance of the concrete. However, current carriers suffer from poor mechanical properties, poor compatibility with cement-based materials, and high costs. This study proposed a crack-self-healing concrete based on a mixed culture of microorganisms immobilized in recycled aggregate, and investigated the effects of the time of recycled aggregate incorporation on the concrete’s compressive strength and self-healing performance. The results showed that the optimal adsorption and incubation times for the recycled aggregates were 15 min and 9 days, respectively. Following mineralization and reinforcement, the water absorption and crushing index of the recycled aggregates was 11.4% and 20.4%, respectively. Moreover, the precipitates at the concrete cracks were in the form of regular cubes and clusters, and the crystals were calcite and aragonite. Small amounts of phosphorus were detected, originating from extracellular polymers produced by microbial metabolism, indicating that the organic matrix was involved in the crystal nucleation and growth processes. The compressive strength of the concrete increased by 35%. After repair and curing, the crack healing rate of the concrete reinforced with microorganisms immobilized on the recycled aggregates reached 70%. Full article

Calcium- and iron-rich sludge from urban storm sewer is an ideal source of phosphorus adsorbents. This study used urban storm sewer sludge to prepare phosphorus adsorbents via pyrolysis. Comparing adsorbents prepared under different conditions, the optimal material was produced at 800 °C in a nitrogen atmosphere and was named 800N. Analyses were conducted using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller surface area analysis, and X-ray photoelectron spectroscopy. The results showed that 800N is rich in carbon, calcium, and iron. The adsorbent has a pore volume of 0.013 cm³/g and a specific surface area of 3.566 m²/g. Adsorption performance was most effective at a pH of 8, achieving an adsorption capacity (q_e) of 19.32 mg/g and a removal rate of 87.75%. Kinetic and thermodynamic studies revealed that the adsorption of phosphorus by the adsorbent conforms to the pseudo-second-order kinetic model and the Langmuir isotherm model. Based on the characterization results, it can be reasonably inferred that the primary mechanisms involved in phosphorus adsorption by the adsorbent are inner-sphere complexation, ligand exchange, and chemical precipitation. This study offers a novel solution for mitigating phosphorus pollution and promoting the resource utilization of urban storm sewer sludge. Full article

Phosphorus scarcity and inefficient fertilizer utilization highlight the need for sustainable phosphorus recovery and reuse strategies. In this study, a Zn/Fe-layered double hydroxide (Zn/Fe-LDH)-kelp-derived biochar (KBC) composite (Zn/Fe-LDH@0.5KBC) was synthesized via co-precipitation for phosphate capture and subsequent reutilization as a slow-release fertilizer. The incorporation of KBC improved the dispersion of LDH nanosheets and generated a hierarchical porous structure with a specific surface area of 122.13 m²/g. As a result, Zn/Fe-LDH@0.5KBC exhibited a high phosphate adsorption capacity of 132.52 mg P/g and reached adsorption equilibrium within 240 min. Kinetic and isotherm analyses indicated that phosphate adsorption was dominated by chemisorption and was best described by the Sips model. Comprehensive scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses revealed that phosphate removal occurred through synergistic mechanisms, including electrostatic attraction, interlayer anion exchange, surface complexation, and metal phosphate precipitation. The P-loaded composite exhibited diffusion-dominated phosphorus release in soil and significantly enhanced pak choi growth. Compared with the control, labile phosphorus increased from 2.8% to 6.8%, while moderately labile phosphorus increased from 6.3% to 14.1%, indicating improved phosphorus availability. These findings demonstrate an effective strategy for integrating phosphate recovery from wastewater with agricultural reuse and provide insights into the development of multifunctional adsorbent-fertilizer systems for circular phosphorus management. Full article

Hexavalent chromium Cr(VI) is a highly toxic and mobile contaminant commonly detected in industrial effluents and groundwater, requiring efficient and scalable treatment strategies. In this study, a commercial unmodified biochar (UB) and an iron-modified biochar (IMB) were evaluated for Cr(VI) removal from aqueous solutions. Iron modification via FeCl₃ impregnation and alkaline precipitation (pH 9) increased surface iron content from 0.2% to 3.3%, based on Energy Dispersive X-ray (EDX) analysis and extractable Fe from 0.009% to 0.108% (FerroVer). X-ray Diffraction (XRD) analysis suggested the presence of iron-containing phases and Fourier Transform Infrared (FTIR) analysis indicated the appearance of an Fe-O band at 564 cm⁻¹. BET analysis showed a slight decrease in surface area from 359 to 317 m² g⁻¹, consistent with partial pore blockage following iron modification. Batch adsorption experiments (pH 2–10; initial Cr(VI) concentration 5–600 mg L⁻¹; adsorbent dosage 2 g L⁻¹) revealed a maximum Langmuir adsorption capacity of 158 mg g⁻¹ for IMB, nearly double that of UB (82 mg g⁻¹), with optimal performance at pH 4–6. At equilibrium, removal efficiencies of ~60% and ~80% were obtained for UB and IMB, respectively (C₀ = 100 mg L⁻¹; adsorbent dose = 2 g L⁻¹). Kinetics followed a pseudo-second-order model, with IMB reaching equilibrium within 8 h compared to 50 h for UB. Isotherm analysis is consistent with Langmuir behavior for UB and Freundlich behavior for IMB. The improved adsorption performance of IMB is likely associated with the increased iron content introduced during modification, demonstrating its potential as an effective adsorbent for Cr(VI) removal from water. Full article

Red mud (RM) can be used as a fertilizer for large-scale disposal, but its low phosphorus content limits its high-value utilization. This study prepared composites of RM and biogas residue (BR) via co-pyrolysis, and adsorbed phosphorus from biogas effluent to increase the phosphorus content. The results show that composites with 25% BR addition and that were pyrolyzed at 600 °C had the highest phosphate adsorption capacity. Composites with a dosage over 50 g·L⁻¹, pH at 3, and initial phosphate concentration lower than 30 mg·L⁻¹ achieved a theoretical maximum phosphorus adsorption capacity of 2.877 mg·g⁻¹. The surfaces of the composites were enriched with functional groups, such as Fe-O, and this formed the complex of FePO₄ for phosphate adsorption incrementation. RM-BR adsorption of phosphate satisfied the pseudo-second-order kinetic equation, and the adsorption constant was up to 0.9949. The adsorption results of phosphorus by the composites can also be well fitted by the Langmuir models (R² = 0.969 and 0.991), indicating that the composites were more inclined to a monolayer adsorption mode. Thus, chemical precipitation was the major way for phosphate adsorption. Furthermore, the environmental impact of the biogas slurry that was disposed of with the composites in this study was lower compared to the traditional coagulation precipitation process. Above all, this study established a practical method for adsorbent preparation of RM for phosphorus recovery from biogas slurry. Full article

The co-contamination of manganese ions (Mn²⁺) and ammonia nitrogen (NH₄⁺) caused by the stockpiling of manganese residue poses a serious threat to the ecological environment. In this study, a series of the composite was prepared from red mud, bentonite, and corn straw via oxygen-limited pyrolysis. The effects of pyrolysis temperature and raw material ratio on the material properties were investigated, and the synergistic remediation performance of the composites for Mn²⁺ and NH₄⁺ in manganese residue-contaminated soil was evaluated through a 180-day soil column experiment. The results showed that the composite prepared with a raw material ratio of 1:1:1 at a pyrolysis temperature of 700 °C exhibited the largest specific surface area and the most developed pore structure, achieving a Mn²⁺ removal rate of 92.72% ± 0.85% in aqueous solution. In the soil column experiment, the material prepared at 700 °C gave the highest immobilization rate for soil Mn²⁺ (96.22% ± 0.5%), whereas the combined addition of materials prepared at 700 °C and 500 °C achieved the best removal efficiency for NH₄⁺ (99.33% ± 0.23%). Mechanistic studies revealed that the stabilization of Mn²⁺ is primarily attributable to alkaline precipitation and mineral lattice solid solution induced by the composite, leading to the formation of stable spinel phases (e.g., (Fe,Mn)₃O₄) and insoluble manganese phosphate-carbonate salts. The removal of NH₄⁺ is proposed to proceed via adsorptive enrichment by the porous structure and Fe⁰-mediated Fenton-like catalytic oxidation, ultimately converting NH₄⁺ to N₂ gas. The 180-day monitoring results demonstrated that the remediation effect continuously increased over time, indicating good long-term stability of the composite. This study provides an efficient, low-cost functional material derived from solid waste for the remediation of manganese residue-contaminated soil and offers a theoretical basis for the synergistic resource utilization of multiple solid wastes. Full article

This work describes the development of a core–shell magnetic nanoadsorbent (Fe₃O₄@TiO₂) designed for the selective recovery of rare earth elements (REEs) from electronic waste. The synthesis involved the co-precipitation of magnetite coated with an anatase-phase TiO₂ layer, subsequently functionalized with organophosphorus groups using glycolic acid and phosphoric acid. This surface modification, verified via FT-IR spectroscopy and zeta potential analysis, provided the material with a high density of active sites. Adsorption studies with lanthanum revealed that the process follows pseudo-second-order kinetics, reaching equilibrium in only 15 min with a theoretical model-calculated capacity of 19.4 ± 0.8 mg/g at pH 5. The material demonstrated high stability and reusability, maintaining 75% of its adsorption capacity after five cycles with a corresponding H₂SO₄ desorption efficiency of 58–60%. Finally, the nanoadsorbent was validated on real LCD screen leachates following an upstream pH 5.0 pre-neutralization and filtration stage designed to remove massive baseline concentrations of iron and copper. Although residual copper and chromium acted as the primary competitors within the remaining complex matrix, the material effectively partitioned REEs (Gd, Y, Ce, Pr, Nd, and Sm) present at ultra-low trace levels (μg/L), demonstrating its potential for urban mining and the circular economy. Full article

Industrial wastewater containing synthetic dyes is difficult to treat because many dyes are chemically stable, highly colored, and resistant to natural degradation. In this study, a Ag₂CO₃/montmorillonite (Ag₂CO₃/MMT) composite photocatalyst was synthesized by an in situ precipitation method using acid-activated MMT as a low-cost clay support. The prepared material was characterized by XRD, FTIR, SEM, BET, and UV–Vis diffuse reflectance spectroscopy to evaluate its structural, morphological, textural, and optical properties. XRD and FTIR confirmed the formation of crystalline Ag₂CO₃ on the MMT support, while SEM analysis showed dispersed Ag₂CO₃ surface particles/deposits on the clay sheets. BET analysis indicated that the composite retained mesoporosity after Ag₂CO₃ deposition, which is beneficial for dye adsorption and diffusion. The photocatalytic performance was evaluated using methylene blue (MB) and methyl orange (MO) under visible-light irradiation. The Ag₂CO₃/MMT composite showed efficient dye decolorization, with faster degradation of cationic MB than anionic MO, mainly due to stronger electrostatic interaction between MB and the negatively charged catalyst surface. Kinetic analysis followed a pseudo-first-order model, with apparent rate constants of 0.036 min⁻¹ for MB and 0.021 min⁻¹ for MO. Operational parameters, including solution pH, irradiation time, and catalyst dosage, strongly influenced photocatalytic efficiency. Reactive species trapping experiments indicated that superoxide radicals (•O₂⁻) and photogenerated holes (h⁺) were the dominant oxidative species. The catalyst retained more than 91% activity after four cycles, indicating good recyclability under the tested conditions. These results suggest that Ag₂CO₃/MMT is a promising visible-light-responsive photocatalyst for dye-contaminated wastewater treatment. Full article

China is rich in high-sulfur natural gas resources. During reservoir development, reservoir temperature and pressure reduction induces the precipitation of elemental sulfur. Subsurface sulfur deposition seriously affects the recovery and the stable production of high-sulfur gas reservoirs. This study utilized multiple experimental techniques, including CT scanning, scanning electron microscopy, energy spectrum analysis, and nuclear magnetic resonance. The experiments were conducted under different water saturation levels and pressure differences. The results showed that the permeability of the rock samples decreased after sulfur deposition. The permeability reduction varied from 0.004 mD to 8.852 mD, with a relative change of 10.2% to 29.8%. Meanwhile, sample porosity also declined, and the porosity damage ranged from 1.5% to 11.9%. Scanning electron microscopy showed that sulfur presented a membrane adsorption morphology on the surface of skeleton particles, with spherical particles protruding from the membrane. Rock samples with poorer physical properties showed lamellar superposition sulfur deposition. Sulfur deposition damage became more severe with increasing pressure difference and weakened as water saturation increased. Beyond a water saturation of 40.6%, further increases no longer reduce sulfur deposition damage. Full article

Haze Pollution in China arises from the rapid enlargement of ultrafine particles into light-absorbing fine particulate matter through adsorption processes under atmospheric stagnation conditions. This study focuses on the sources of ultrafine particles (UFPs), the most critical component of haze pollutants during severe pollution periods in China. Utilizing methods including the spatial Durbin model and statistical data for the 28 cities (the “2 + 26” cities) within the Beijing–Tianjin–Hebei air pollution transmission channel—suffering the most severe haze pollution—it investigates the impact of pollution-intensive industries on haze pollution. This study reveals several key findings regarding China’s haze pollution. First, the principal source of ultrafine particles within China’s haze stems from the desulfurization, denitrification, and dust removal processes of pollution-intensive industries (the direct effect of these industries on haze is 0.028 * according to the SDM regression results). Crucially, the specific operational factors driving the abrupt increase in atmospheric UFPs during severe haze periods in China are identified as extensive management practices in desulfurization, the progressive tightening and annual escalation of denitrification emission standards, and the reliance on electrostatic precipitation which is ineffective against ultrafine particles. Second, haze pollution predominantly occurs in regions characterized by concentrations of pollution-intensive industries coupled with weak atmospheric environmental self-purification capacity (this carrying capacity for pollution-intensive industries exerts a significant negative impact on haze, demonstrated by a direct effect of −0.020 **; further analysis reveals that this is caused by regional differences in atmospheric self-purification capacity). Third, regional air transport acts as a contributing source, introducing UFPs from neighboring areas into local haze pollution, reflected by an indirect effect of pollution-intensive industries of 0.151 ** stemming from such spatial spillovers. Based on these conclusions, the study proposes a set of policy recommendations: relocate pollution-intensive industries using a gradient approach based on atmospheric self-purification capacity differences; systematically upgrade wet flue gas desulfurization technologies for industrial emissions; effectively promote technological innovation in denitrification processes; implement scientific controls on ammonia emissions; strengthen R&D in core technologies for UFP removal; innovate dust removal technologies to enhance overall system efficiency; reinforce regional coordinated governance; implement targeted training programs and select qualified management personnel; systematically enhance the environmental management capabilities of staff; and effectively mitigate the spillover effects of haze pollution. Full article