Search Results (93)

Highly sensitive real-time detection of hydrogen sulfide (H₂S) is important for human health and environmental protection due to its highly toxic properties. The development of high-performance H₂S sensors remains challenging for poor selectivity, high limit detection and slow recovery from irreversible sulfidation. To solve these problems, we strategically prepared a layered structure of CuO-sensitized WO₃ flower-like hollow spheres with CuO as the sensitizing component. A 15 wt% CuO/WO₃ exhibits an ultra-high response (R_a/R_g = 571) to 10 ppm H₂S (131-times of pure WO₃), excellent selectivity (97-times higher than 100 ppm interference gas), and a low detection limit (100 ppb). Notably, its fast response (4 s) is accompanied by full recovery within 236 s. After 30 days of continuous testing, the response of 15 wt% CuO/WO₃ decreased slightly but maintained the initial response of 90.5%. The improved performance is attributed to (1) the p-n heterojunction formed between CuO and WO₃ optimizes the energy band structure and enriches the chemisorption sites for H₂S; (2) the reaction of H₂S with CuO generates highly conductive CuS, which significantly reduces the interfacial resistance; and (3) the hierarchical flowery hollow microsphere structure, heterojunction, and oxygen vacancy synergistically promote the desorption. This work provides a high-performance H₂S gas sensor that balances response, selectivity, and response/recovery kinetics. Full article

This study investigates the potential of sulfuric acid modified wheat straw, polysaccharide-rich agricultural byproduct, as a low-cost adsorbent for the selective adsorption of Au(III) ions from aqueous solutions. The wheat straw was treated with concentrated sulfuric acid to enhance its surface properties and functional groups, particularly sulfonic and oxygen-containing functional groups. Adsorption experiments were performed under various conditions, including acid concentrations ranging from 1.0 to 3.0 mol/L, contact times from 1 to 6 h, and initial Au(III) concentrations of 60.36, 90.0, and 150.0 mg/L. The highest adsorption efficiency, 99.0%, was achieved at an acid concentration of 1.0 mol/L. Furthermore, it was determined that an increase in the initial Au(III) concentration from 60.36 mg/L to 150.0 mg/L resulted in a 4.5 times increase in maximum adsorption capacity under optimal conditions. Kinetic modeling revealed that the adsorption process followed pseudo-second order kinetics, suggesting chemisorption as the rate-limiting step. Characterization techniques such as SEM/EDS, XRD, BET and XPS confirmed structural modification, surface sulfonating, and the successful adsorption and reduction of Au(III) to elemental gold (Au⁰) on the modified straw surface. This work demonstrates that modified wheat straw is a promising, effective, and low cost for the recovery of gold from low-concentration solutions and provides insight into the adsorption and reduction mechanisms at the molecular level. Full article

In designing an optimized activated carbon-based adsorbent, several key factors are crucial for its practical application in the industrial sector, including high BET surface area, strong adsorption capacity, selectivity, mechanical and thermal stability, regeneration potential, environmental impact, and cost-effectiveness. This study explores the innovative approach of combining two chemical activating agents, potassium carbonate and sodium thiosulfate, to produce activated carbon with enhanced properties for improved mercury removal. At an activation temperature of 800 °C, the resulting adsorbent achieved a BET surface area of 2132.7 m²/g and a total pore volume of 1.08 cm³/g. Testing its mercury removal efficiency, the maximum adsorption capacity was 289 mg/g at room temperature. The Langmuir isotherm provided an excellent fit to the experimental data, indicating a monolayer adsorption process. Kinetic modeling revealed that the adsorption followed a pseudo-second-order model, consistent with chemisorption. The primary removal mechanism was found to involve complexation of mercury with oxygen and sulfur-containing functional groups, along with pore-filling physical adsorption. The adsorbent also showed a strong affinity for mercury even in the presence of other competing heavy metals. Furthermore, regeneration studies demonstrated the adsorbent’s effectiveness over five cycles. This research introduces a novel, environmentally friendly, and cost-efficient adsorbent for mercury removal. Full article

This study explores the utilization of waste grape pomace-derived hydrochar as an efficient adsorbent for lead (Pb²⁺) removal from aqueous solutions. Hydrochar was produced via hydrothermal carbonization (HTC) at 220 °C, followed by doping with magnesium and iron salts, and subsequent pyrolysis at 300 °C to obtain Fe/Mg-pyro-hydrochar (FeMg-PHC). The material’s structural and morphological changes after Pb²⁺ adsorption were examined using FTIR. FTIR revealed chemisorption and ion exchange as key mechanisms, shown by decreased hydroxyl, carbonyl, and metal–oxygen peaks after Pb²⁺ adsorption. Adsorption tests under varying pH, contact time, and initial Pb²⁺ concentrations revealed optimal removal at pH 5. Kinetic modeling indicated that the process follows a pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm analysis showed that the Sips model best describes the equilibrium, with a maximum theoretical adsorption capacity of 157.24 mg/g. Overall, the simple two-step synthesis—HTC followed by pyrolysis—combined with metal doping yields a highly effective and sustainable adsorbent for Pb²⁺ ion removal from wastewater. Full article

To develop eco-friendly low-temperature NH₃-SCR catalysts for the non-electric industry, a series of CeMn-modified Ba₂Ti₅O₁₂ catalysts were synthesized using the sol-gel method to achieve denitrification. Activity tests revealed that Ce-Mn-modified Ba₂Ti₅O₁₂ catalysts exhibit excellent low-temperature denitrification performance with a broad operational temperature window. Characterization through XRD, XPS, BET, NH₃-TPD, and EPR indicated that Ce-Mn modification enhances surface oxygen chemisorption and increases acidity, significantly improving NO_x reduction. Notably, the optimal catalyst achieved NO_x conversion rates exceeding 90% within the temperature range of 90 to 240 °C under a gas hourly space velocity (GHSV) of 28,000 h⁻¹. In particular, the coexistence of Ce and Mn species promotes the oxidation of NO to NO₂, facilitating the “fast SCR” reaction. The abundance of valence states further enhances the catalyst’s ultra-low-temperature NH₃-SCR denitration performance. Full article

CO₂ capture by adsorption on proper solid materials appears to be a promising approach, due to its low energy requirements and ease of implementation. This study aimed to prepare efficient materials for CO₂ capture based on composites of nanocarbon and reduced graphene oxide, using graphite, L-ascorbic acid, and glycine as precursors. The materials were characterized by XRD, low-temperature N₂ adsorption, FTIR, Raman, and XPS spectroscopies, along with SEM and TEM. The CO₂ adsorption capacities, heats of adsorption, and selectivity were determined. A hierarchical porous structure was found for NC-LAA, NC/RGO-LAA, and NC/RGO-Gly. At 273 K and 100 kPa, the adsorption capacities for NC-LAA and NC-Gly reached 2.6 mmol/g and 2.5 mmol/g, respectively, while for the composites, the capacities were 1.7 mmol/g for NC/RGO-Gly and 3.5 mmol/g for NC/RGO-LAA. The adsorption ability of the glycine-derived materials is related to the presence of nitrogen-containing functional groups. The heats of adsorption for NC-LAA, NC-Gly, and NC/RGO-Gly reveal chemisorption with CO₂. Except for chemisorption, the NC/RGO-LAA material shows a sustained physical adsorption up to higher CO₂ coverage. The best adsorption of CO₂, observed for NC/RGO-LAA, is connected with the synergy between carbon dots and RGO. This composition ensures both sufficient oxygen surface functionalization and a proper hierarchical porous structure. Full article

Apricot kernel shells were evaluated as a sustainable activated carbon precursor for wastewater treatment using experimental and theoretical methods. Two adsorbents were synthesized: physically activated with CO₂ (AKS-CO₂) and chemically activated with H₃PO₄ (AKS-H₃PO₄). Comprehensive materials characterization and adsorption tests using Pb²⁺ ions and Rhodamine B dye (RhB) as model pollutants revealed that AKS-H₃PO₄ significantly outperformed its physically activated counterpart. With an exceptionally high specific surface area (1159.4 m²/g) enriched with phosphorus-containing functional groups, the chemically activated carbon demonstrated outstanding removal efficiencies of 85.1% for Pb²⁺ and 80.3% for RhB. Kinetic studies showed Pb²⁺ adsorption followed pseudo-second-order kinetics, indicating chemisorption, while RhB adsorption fitted pseudo-first-order kinetics, suggesting intra-particle diffusion control. The thermodynamic analysis confirmed the spontaneity of both processes: Pb²⁺ adsorption was exothermic under standard conditions with positive isosteric heat at higher concentrations, reinforcing its chemisorption nature, whereas RhB adsorption was endothermic, consistent with physisorption. Density Functional Theory (DFT) calculations further elucidated the mechanisms, revealing that Pb²⁺ preferentially binds to oxygen-containing functional groups, while RhB interacts through hydrogen bonding and π–π stacking. These findings establish chemically activated apricot kernel shell carbon as a high-performance adsorbent, exhibiting exceptional removal capacity for both ionic and molecular contaminants through distinct adsorption mechanisms. Full article

The rapid pace of industrialization has led to widespread heavy metal contamination in water and soil, highlighting the need for efficient remediation strategies. Among various approaches, adsorption has proven to be an effective method for treating contaminated environments. Layered double hydroxide (LDH) is frequently used in such applications. However, its adsorption efficiency remains limited. In this study, glutamic acid diacetate tetrasodium salt (GLDA) was incorporated into ZnAl LDH via a straightforward co-precipitation and ion exchange method, yielding a modified material, GLDA-LDH, which was subsequently applied for the adsorption of Pb(II) and Cd(II). Adsorption behavior was investigated through kinetic and isothermal models, with results indicating that the process followed pseudo-second-order kinetics and fit well with the Langmuir isotherm, suggesting chemisorption onto monolayer surface. The maximum adsorption capacities reached 219.2 mg/g for Pb(II) and 121.9 mg/g for Cd(II). Furthermore, GLDA-LDH exhibited a strong retention capability for metal ions with minimal desorption and remained effective in the presence of hard water and contaminated soils. XPS analysis revealed distinct interaction mechanisms; surface oxygen and carboxyl groups played a key role in Pb(II) adsorption, whereas nitrogen coordination was involved in Cd(II) uptake. These results point to the potential of GLDA-LDH as a reliable material for addressing heavy metal pollution and provide insights into the design of enhanced LDH-based adsorbents. Full article

Rhodamine B dye is a hazardous pollutant that poses significant risks to human health and aquatic ecosystems due to its toxic, carcinogenic nature and high chemical stability. To address this issue, analcime@nickel orthosilicate nanocomposites were synthesized via the hydrothermal method for efficient rhodamine B dye removal. Two nanocomposites were synthesized: EW (without a template) and ET (with polyethylene glycol 400 as a template, followed by calcination at 600 °C for 5 h). X-ray diffraction (XRD) confirmed the formation of analcime (NaAlSi₂O₆) and nickel orthosilicate (Ni₂SiO₄), with crystallite sizes of 72.93 nm (EW) and 63.60 nm (ET). Energy-dispersive X-ray spectroscopy (EDX) showed distinct distributions of oxygen, sodium, aluminum, silicon, and nickel. Field-emission scanning electron microscopy (FE-SEM) revealed irregular morphology for EW and uniform spherical nanoparticles for ET. The maximum adsorption capacities (Q_max) were 174.83 mg/g for EW and 210.53 mg/g for ET. Adsorption followed the pseudo-second-order kinetic model and was best described by the Langmuir isotherm, indicating monolayer chemisorption. Thermodynamic studies showed that adsorption was exothermic (ΔH = −45.62 to −50.92 kJ/mol) and spontaneous (ΔG < 0) and involved an entropy increase (ΔS = +0.1441 to +0.1569 kJ/mol·K). These findings demonstrate the superior adsorption efficiency of the ET composite and its potential application in dye-contaminated wastewater treatment. Full article

The efficient removal of pharmaceuticals and personal care products (PPCPs) from aqueous solutions using conventional adsorbents is hindered by low adsorption capacity, insufficient selectivity, poor regeneration performance, and limited stability. In this study, a multilayer β-CD/GO membrane was successfully prepared via layer-by-layer coating with β-cyclodextrin (β-CD) and graphene oxide (GO). The multilayer β-CD/GO membrane combines the host–guest complexation ability of β-CD with the abundant oxygen-containing functional groups of GO to enhance the targeted removal of PPCPs (CTD, SMZ, and DCF) from aqueous solutions. The prepared multilayer β-CD/GO membrane adsorbent overcomes the separation difficulties and poor regeneration performance of powdered adsorbents, and the multilayer structure can significantly enhance structural stability and increase the number of adsorption sites. Batch adsorption experiments showed that the optimal adsorption performance of the multilayer β-CD/GO membrane for PPCPs occurred at pH 4 and in the absence of coexisting ions. With increasing pH values in the range of 4–9, the adsorption capacities of CTD, SMZ, and DCF slightly decreased to 14.37, 13.69, and 13.01 mg/g, respectively, and the adsorption capacities decreased slowly to 4.88, 3.51, and 3.26 mg/g as the coexisting ion concentrations increased from 0 to 0.20 mol/L. The adsorption mechanism of the multilayer β-CD/GO membrane for PPCPs was systematically investigated through adsorption kinetics, isotherms, and thermodynamics. The adsorption processes of CTD, SMZ, and DCF by the multilayer β-CD/GO membrane were well described by both pseudo-first-order and pseudo-second-order kinetic models (R² > 0.984), suggesting a hybrid adsorption mechanism involving both physisorption and chemisorption. The isotherm results indicated that the adsorption of CTD by the multilayer β-CD/GO membrane followed the Langmuir model (R² = 0.923), whereas the adsorption of SMZ and DCF was better described by the Freundlich model (R² = 0.984–0.988). The multilayer β-CD/GO membrane exhibited high adsorption capacities for CTD, SMZ, and DCF with maximum capacities of 35.56, 43.29, and 39.49 mg/g, respectively. Thermodynamic analyses indicated that the adsorption of PPCPs was exothermic ($\Delta H^0$ = −86.16 to −218.49 J/mol/K) and non-spontaneous ($\Delta G^0$ = 9.84–11.56, 9.50–12.54, and 10.09–14.46 kJ/mol). The multilayer β-CD/GO membrane maintained a removal efficiency of over 58.45–71.73% for CTD, SMZ, and DCF after five consecutive regeneration cycles, demonstrating high reusability for practical applications. The adsorption mechanisms of the multilayer β-CD/GO membrane include electrostatic interactions, hydrogen bonding, hydrophobic interactions, and π-π EDA interactions. This study offers a promising and environmentally friendly adsorbent for the efficient removal of PPCPs from aqueous solutions. Full article

This study examines the potential of phosphogypsum—a by-product of the phosphoric acid production process—as a low-cost and sustainable adsorbent for the removal of crystal violet dye from aqueous solutions. Phosphogypsum was characterized using X-ray fluorescence, X-ray diffraction, particle size distribution, and zeta potential measurements, revealing that it is primarily composed of di-hydrate calcium sulfate, with a negatively charged surface in the pH range from 1.8 to 8.2 and a mean particle size of 12.2 microns. Experiments were conducted to evaluate the effects of pH, adsorbent dose, contact time, and temperature on its adsorption ability. The results indicated that the adsorption capacity increased with the pH up to a value of 5, while higher initial dye concentrations enhanced the uptake capacity but reduced the removal efficiency. The adsorption process was well described by the Langmuir isotherm, suggesting chemisorption as the dominant mechanism, while the pseudo-second-order kinetic model indicated that adsorption primarily occurred on the exterior surface. The thermodynamic analysis revealed that the process was exothermic and spontaneous at 20 °C and 30 °C, with a decrease in favorability at higher temperatures. The adsorbent demonstrated reusability, with a removal efficiency of 71% after five regeneration cycles. Furthermore, phosphogypsum was successfully applied to treat real textile effluent, achieving significant reductions in both biochemical oxygen demand (71%) and dye content (87%). These findings highlight the potential of phosphogypsum as an effective and eco-friendly adsorbent for wastewater treatment, contributing to waste valorization and environmental sustainability. Full article

Tannic acid (TA), a prevalent polyphenolic contaminant in industrial effluents, significantly inhibits microbial activity in anaerobic digestion, thereby diminishing wastewater treatment efficiency. In this study, a sulfidized nano zero-valent iron (S-nZVI) composite incorporated into sludge biochar (SB), abbreviated as SB-S-nZVI, was synthesized via a one-step hydrothermal method. The composite’s adsorption capacity for TA and its impact on anaerobic digestion were systematically evaluated. Experimental results showed that SB-S-nZVI achieved a TA removal efficiency of 99.31% under optimal conditions (S/Fe = 0.05, dosage = 0.3 g·L⁻¹), with a maximum adsorption capacity of 337.08 mg·g⁻¹. In anaerobic digestion, the addition of 0.03 g·L⁻¹ SB-S-nZVI enhanced chemical oxygen demand (COD) removal by 3.32%, increased specific methanogenic activity by 62.66%, and improved the microbial community composition, particularly enriching hydrolytic bacteria (Georgenia) and methanogenic archaea (Methanosaeta). The mechanistic analysis revealed that the FeS protective layer of SB-S-nZVI inhibited nano zero-valent iron oxidation and facilitated chemisorption-driven TA removal. This study presents an innovative approach for the integrated treatment of TA-contaminated wastewater by combining adsorption, degradation, and energy recovery. Full article

The treatment of wastewater using microalgae is regarded as a green and potential technology. However, its engineering application has been largely hindered because of the limitation of microalgae separation and harvesting. Therefore, immobilization technology has been widely used to embed microalgae for wastewater treatment. In this paper, sodium alginate (SA) and polyvinyl alcohol (PVA) as the common immobilized carriers were used to immobilize ankistrodesmus falcatus for simulated slaughtering wastewater (SSW) treatment. The experimental results of the mass transfer and adsorption of immobilized carriers were found to show that the mass transfer of SA-SiO₂ gel balls (SS-GB) was better than PVA-SA gel balls (PS-GB) and that the adsorption of PS-GB was better than SS-GB. When immobilizing microalgae with the two kinds of carriers, it was found that SA-SiO₂ microalgal spheres (SS-MS) were better than PVA-SA microalgal spheres (PS-MS) for the maintenance of microalgal cell activity and that PS-MS were better than SS-MS for the resistance to biodegradation. This is because the carrier of PS-MS had a thick shell and dense structure, while the carrier of SS-MS had a thin shell and loose structure. The results of SSW treatment by PS-MS and SS-MS were found to show that the total phosphorus (TP) removal rates of PS-MS and SS-MS were 90.31% and 86.60%, respectively. This indicates that the TP removal effect of PS-MS was superior to that of SS-MS. The adsorption kinetics simulation showed that the adsorption of TP onto PS-GB was controlled by chemisorption and that the adsorption of TP onto SS-GB was controlled by physical adsorption. The chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) removal of PS-MS were 9.30% and 10.70%, respectively, and the COD and NH₄⁺-N removal of SS-MS were 54.60% and 62.08%, respectively. This indicates that the COD and NH₄⁺-N removal effect of SS-MS were superior to PS-MS. This is the result of the combined action of the degradation by microalgal cells and adsorption by the carrier. Full article

Biochar is a potential material for making slow-releasing phosphorus (P) fertilizers for the sake of increasing soil P-use efficiency. The adsorption of phosphorus by pineapple leaf biochar (PB) prepared at different pyrolysis temperatures and its mechanism remain unclear. In order to study the effect of preparation temperature on the structural characteristics of biochar from pineapple leaves and the adsorption of phosphorus by biochar, pineapple leaves were used as raw materials to prepare biochar by restricting oxygen supply at 300 °C, 500 °C, and 700 °C. The structural characteristics and adsorption of phosphorus by pineapple leaf biochar at different temperatures (PB300, PB500, and PB700) were analyzed. The results showed the following: (1) The pore structure of biochar pyrolysis at 300 °C (PB300) did not significantly change, while the surface structure of biochar pyrolysis at 700 °C (PB700) significantly changed, the specific surface area (S_BET) increased by 26.91~37.10 times that observed in PB300 and PB500, and the pore wall became thinner. (2) The number of functional groups (C=O) in PB700 decreased, and the relative content of C-H/-CHO in PB500 and PB700 increased by 4.38 times that observed in PB300. (3) The adsorption of phosphorus by biochar was a multi-molecular layer chemisorption, accompanied by single-molecular-layer physical adsorption and intramolecular diffusion. For PB300, both the physical and chemical processes of the adsorption of PO₄³⁻ by biochar were weakened, and the chemical process was dominated by cationic (Ca²⁺, Mg²⁺, Fe³⁺, and Al³⁺) adsorption at 500 °C. For PB700, the physical adsorption dominated by pore size structure was the main process, and the physicochemical adsorption at 700 °C was significantly stronger than that observed at 300 °C and 500 °C. These results indicate that biochar prepared at 500 °C can save energy in the preparation process and has excellent physical and chemical structure, which can be used as the basic material for further modification and preparation of biochar phosphate fertilizer. Full article

Functionalized nanomaterials with surface-active groups have garnered significant research interest due to their wide-ranging applications, particularly in water treatment for removing various contaminants. This study focuses on developing a novel, multi-functional nanobiosorbent by synthesizing nanosized biochar from artichoke leaves (NBAL) and molybdic acid (MA). The resulting nanobiosorbent, MA@NBAL, is produced through a microwave-irradiation process, offering a promising material for enhanced environmental remediation. The characteristics of assembled MA@NBAL were evaluated from SEM-EDX, XPS, TGA, FT-IR, and zeta potential detection. The size of particles ranged from 18.7 to 23.7 nm. At the same time, the EDX analysis denoted the existence of several major elements with related percentage values of carbon (52.9%), oxygen (27.6%), molybdenum (8.8%), and nitrogen (4.5%) in the assembled MA@NBAL nanobiosorbent. The effectiveness of MA@NBAL in removing Hg(II) ions was monitored via the batch study method. The optimized maximum removal capacity of Hg(II) ions onto MA@NBAL was established at pH 6.0, 30.0 min equilibrium time, and 20 mg of nanobiosorbent, providing 1444.25 mg/g with a 10.0 mmol/L concentration of Hg(II). Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, with R² values ranging from 0.993 to 0.999 for the two tested Hg(II) concentrations, indicating excellent alignment with the experimental data. This suggests that the chemisorption mechanism involves cation exchange and complex formation. Isotherm model evaluation further confirmed the adsorption mechanism, with the Freundlich model providing the best fit, yielding an R² of 0.962. This result indicates that Hg(II) adsorption onto the surface of MA@NBAL nanobiosorbent occurs on a heterogeneous surface with multilayer formation characteristics. The results of the temperature factor and computation of the thermodynamic parameters referred to endothermic behavior via a nonspontaneous process. Finally, the valid applicability of MA@NBAL nanobiosorbent in the adsorptive recovery of 2.0 and 5.0 µg/mL Hg(II) from contaminated real aquatic matrices was explored in this study, providing 91.2–98.6% removal efficiency. Full article