Search Results (172)

Spent automobile catalysts can be an important source of platinum for industry applications. Low-cost and simple technologies for platinum recovery from this source are sought, especially involving the application of green adsorbents. Honeycomb biowaste can be an excellent candidate for this purpose; n-hexane-treated honeycomb biowaste is therefore obtained for the first time. This material is characterized using several instrumental techniques, confirming the presence of O, N, and P heteroatoms on its surface and the complex morphology of its particles. The maximum static Pt(II)/Pt(IV) adsorption (46 mg/g and 60 mg/g, respectively) onto the n-hexane-extracted honeycomb biomass is reached at pH = 1.55 and a contact time of 50 h. The adsorption kinetics are best fitted to the pseudo-second-order model in both cases. The Langmuir model best described the Pt(II)/Pt(IV) adsorption isotherms on the studied material. Quantitative desorption of the Pt from the studied material is reached for 1 mol/L thiourea dissolved in HCl. The adsorption mechanism of Pt(IV) ions onto the obtained material is based mainly on the surface complexation reactions. The studied material is successfully applied for the first time for Pt(IV) removal from a spent automobile catalyst leachate. Full article

To ensure the sustainable use of limited resources, it is essential to establish selective and efficient recycling technologies for platinum group metals (PGMs). This study focused on the selective precipitation-based separation of Pt(IV) from hydrochloric acid (HCl) solutions in the presence of various metal ions, using trans-1,4-bis(aminomethyl)cyclohexane (BACT) as a precipitating agent. By using BACT, we succeeded in the selective separation of Pt(IV) by precipitation from HCl solutions containing Pd(II) and Rh(III). Notably, selective and efficient recovery of Pt(IV) was accomplished across various HCl concentrations, with a small amount of BACT and within a short shaking time. To evaluate the practical applicability of the method, Pt(IV) was recovered and purified from the HCl leachate of spent automotive exhaust gas purification catalysts using BACT. As a result, a high Pt recovery of 95.6% and a high purity of 99.3% were achieved. Although Pt(IV) was recovered as a precipitate containing BACT, it was found that Pt black could be readily obtained by dissolving the precipitate in HCl solution followed by reduction with sodium borohydride. Detailed structural analysis of the Pt(IV)-containing precipitate revealed that it is an ionic crystal composed of [PtCl₆]²⁻ and protonated BACT. The selective formation of this ionic crystal in HCl solution, along with its stability under such conditions, is the key to the selective recovery of Pt(IV) using BACT. Full article

This study addresses the efficiency and cost challenges of hydrogen evolution reaction (HER) catalysts in the context of carbon neutrality strategies by employing a synergistic approach that combines cation vacancy anchoring and transition metal doping on two-dimensional (2D) MXenes. Using an in situ LiF/HCl etching process, the aluminum layers in Ti₃AlC₂ were precisely removed, resulting in a few-layer Ti₃C₂T_x MXene with an increased interlayer spacing of 12.3 Å. Doping with the transition metals Fe, Co, Ni, and Cu demonstrated that Fe@Ti₃C₂ provided the optimal HER performance, characterized by an overpotential (η₁₀) of 81 mV at 10 mA cm⁻², a low Tafel slope of 33.03 mV dec⁻¹, and the lowest charge transfer resistance (R_ct = 5.6 Ω cm²). Mechanistic investigations revealed that Fe’s 3d⁶ electrons induce an upward shift in the d-band center of MXene, improving hydrogen adsorption free energy and reducing lattice distortion. This research lays a solid foundation for the design of non-precious metal catalysts using MXenes and highlights future avenues in bimetallic synergy and scalability. Full article

This work concerns the preparation of Pt/AC catalysts (Pt supported on activated carbon) and their application to the synthesis of hydrocarbon biofuels through the HEFA (hydroprocessing of esters and fatty acids) route. The key motivation for the work was that catalysts based on sulfided Mo supported on γ-Al₂O₃, traditionally employed in the hydroprocessing of petroleum derivatives, (i) are unstable in the HDO (hydrodeoxygenation) of biomass-derived feedstocks and (ii) can contaminate the resulting biofuels with sulfur. In this context, a systematic study on the effects of preparation conditions on the properties of the resulting Pt/AC catalysts and their performance in HEFA was carried out for the first time. Efficient catalysts were obtained, which led to the complete deoxygenation of lauric acid and coconut oil, yielding products composed primarily of n-alkanes. The highest HDO activity was verified for the catalyst prepared using as a support an AC previously subjected to thermal treatment up to 800 °C in a H₂ atmosphere (which removed most of the surface acidic oxygenated groups), depositing Pt over the surface of this support via wet impregnation using a H₂PtCl₆ solution acidified with HCl. The obtained results showed the great potential of the Pt/AC catalysts for the production of hydrocarbon biofuels through the HEFA route. Full article

In this study, a vanadyl phthalocyanine was synthesized and characterized using XRD, FTIR, and XPS, confirming the successful metalation of the phthalocyanine ring. XRD analysis showed the vanadyl phthalocyanine crystallized in the P-1 crystal lattice, with unit cell parameters a = 12.058 Å, b = 12.598 Å, and c = 8.719 Å, and the lattice angels were 96.203°, 94.941°, and 68.204°. FTIR spectroscopy supported the metalation by the disappearance of the N-H stretch of the non-metalated phthalocyanine. The vanadyl phthalocyanine was tested as a heterogenous catalyst for the conversion of fructose into methyl levulinate in H₂SO₄–methanol and HCl–methanol systems. The H₂SO₄–methanol reaction system catalyzed with the vanadyl phthalocyanine, and a zeroth-order rate constant of 1.10 × 10⁻⁶ M/s was observed, which was 1.74 times faster than sulfuric acid alone. The HCl–methanol system showed a zeroth-order of reaction with a rate constant of 2.33 × 10⁻⁶ M/s, which was 1.3 times faster than the HCl–methanol alone. While the HCl–methanol system showed a faster reaction rate, product distribution favored methyl levulinate formation in the H₂SO₄–methanol system. The main products identified were methyl levulinate and hepta-2,4-dienoic acid methyl ester, with a minor amount of hydroxymethylfurfural formed. These results suggest that vanadyl phthalocyanine can be effectively used as a catalyst to increase the rate of fructose conversion to methyl levulinate in either H₂SO₄ or HCl–methanol. Full article

A superhydrophilic silica coating was prepared using a sequential dipping process involving acid-catalyzed silica, base-catalyzed silica, and 3-(trihydroxysilyl)propanesulfonic acid. Acid-catalyzed and base-catalyzed silica particles with varying diameters were synthesized by hydrolyzing tetraethyl orthosilicate using HCl and NH₃·H₂O as catalysts, respectively. 3-(Trihydroxysilyl)propanesulfonic acid was obtained by oxidizing mercaptopropyl trimethoxysilane with hydrogen peroxide under acidic conditions. The resulting silica coating exhibited exceptional superhydrophilicity, with a water static contact angle of 5.0°, and demonstrated underwater superoleophobicity, with a hexadecane underwater contact angle exceeding 140°. Surfaces coated with the superhydrophilic silica coatings showed excellent performances in oil–water separation, anti-protein adsorption, and anti-fogging applications. Full article

This study examined the hierarchical structuring of *BEA zeolite using two distinct approaches: double aluminum removal with solid ammonium hexafluorosilicate (2x-AHFS) and a solution of 0.2 M sodium hydroxide followed by 0.5 M hydrochloric acid (T-NaOH). Additionally, niobium pentoxide (Nb₂O₅) was impregnated at different loadings (5, 10, 15, and 20 wt.%) onto the hierarchized materials. Both treatments increased the SiO₂/Al₂O₃ ratio and produced crystals with domains of about the same size. The hierarchization methods generated secondary mesopores and reduced the micropores in the treated HB zeolite. The solid-state NMR analysis by ²⁷Al and ²⁹Si indicated that the 2x-AHFS treatment increased the hydrophobic character of the zeolite, while the treatment with NaOH/HCl resulted in a less hydrophobic material. A balanced quantity of Brønsted and Lewis sites was observed for all treated zeolites. Thus, these combined physicochemical characteristics of the new catalysts may explain their superior performance in the dehydration reactions. In the case of ethanol dehydration at 230 °C, the 20 wt.% Nb₂O₅ supported on the T-NaOH catalyst produced an 84% conversion and 86% selectivity for ethylene (EE), with 14% diethyl ether (DEE) as the only products. Conversely, in the 1-propanol dehydration reaction, the 20 wt.% Nb₂O₅ supported on 2x-AHFS achieved 99% conversion, producing 99% propene. Full article

The biogas residue (BR) from the anaerobic digestion of sludge poses a threat to the environment due to the presence of toxic and hazardous substances. Furthermore, emerging contaminants, such as bisphenol A (BPA), are widespread in domestic and industrial wastewater, requiring efficient and sustainable treatment technologies. In this study, the BR-based biochar was pyrolyzed from urea-modified BR and employed as a catalyst to activate peroxymonosulfate (PMS) for BPA degradation. With BR-based biochar pyrolyzed at 750 °C as a catalyst, 20 mg/L of BPA was completely removed. Free radical detection confirmed that hydroxyl radical (•OH) and sulfate radical (•SO₄⁻) generation decreased with the increase in catalyst reuse times. The X-ray photoelectron spectra showed that the catalyst deactivation mainly resulted from -COOH and C-OH group loss, which acted as active sites for generating •OH and •SO₄⁻, and HCl or NaOH regeneration for catalysts could recover oxygen-containing functional groups, boosting BPA removal from 54.7% to 91.5% and 100%, respectively. Thermal regeneration could only enlarge the catalyst’s specific surface area (SSA) to recover adsorption capacity, but might not restore the free radical generation capability. This research offered a theoretical basis for the sustainable utilization of BR and provided a reference for reusing catalysts in wastewater treatment. Full article

This study investigated the production of high-performance biochar from swine manure using a sequential carbonization process combining hydrothermal carbonization (HTC) and pyrolysis. Biochar produced through HCl-assisted sequential carbonization exhibited superior properties, including the highest fixed carbon (70.0%), higher heating value (28.48 MJ/kg, ~18.8% increase over HTC-Py), and BET surface area (279.66 m²/g, ~17 times higher than other biochars). These improvements were attributed to the catalytic role of HCl in promoting dehydration, hydrolysis, and decarboxylation, leading to a more condensed and stabilized carbon structure. Furthermore, HCl significantly enhanced heavy metal removal, reducing Zn to 343.17 mg/kg (compared to HTC-Py 1324.15 mg/kg) and lowering Cd, As, Cu, Pb, Ni, and Cr by 70–80%, demonstrating effective demineralization. This approach presents a practical strategy for producing high-quality biochar with improved carbonization, energy properties, and pollutant removal, offering potential applications in environmental and agricultural fields. Full article

The detailed decomposition pathway of ammonium perchlorate (AP) is important for the design of solid propellants containing AP. In this paper, the possible decomposition reactions of AP upon nitrogen-doped graphene (N-Gr) as a catalyst are investigated via density functional theory. The reaction pathways of HClO₄ and NH₃ on the N-Gr surface are explored. The decomposition reaction path of the HClO₄ molecule on the N-Gr is HClO₄ → ${\mathrm{ClO}}_3^{-}$ → ${\mathrm{ClO}}_2^{-}$ → ClO⁻ → Cl⁻. The rate-determining step of the process is the Cl-O bond-breaking reaction of ${\mathrm{ClO}}_2^{-}$ anions, and the activation energy of the reaction is 0.849 eV. The oxidation of the N-Gr surface promotes the decomposition of both HClO₄ and NH₃. The OH groups produced during the decomposition process can promote the adsorption and decomposition of NH₃. This work provides new insights into the decomposition of AP on N-Gr at the molecular level. Full article

The development of a selective separation and recovery method for platinum-group metals (PGMs) is in high demand to establish efficient and practical recycling technologies for different secondary materials such as industrial automobile catalysts. In this study, the highly selective precipitation of Pt(IV) from hydrochloric acid (HCl) solutions containing Pd(II), Pt(IV), and Rh(III) was successfully achieved using m-phenylenediamine dihydrochloride (MPDA) as a precipitant. Pt(IV) selectivity was observed at HCl concentrations higher than 7 M, whereas the co-precipitation of Rh(III) could not be suppressed using 3–7 M HCl solutions. Successful recovery of Pt(IV)-containing precipitates with high Pt yield (94.6%) and Pt purity (98.5%) was also achieved using an actual catalyst leaching solution with a complex composition containing PGMs, base metals, and rare metals. Structural analyses revealed that the Pt(IV)-containing precipitate forms ionic crystals composed of [PtCl₆]²⁻/protonated m-phenylenediamine (MPDA-2H⁺) in a 1:1 ratio. The high stability and insolubility of the Pt(IV)-containing ionic crystals, owing to their highly packed structure, resulted in the highly selective precipitation of Pt(IV) at high HCl concentrations. Full article

In this study, hydrochars loaded with iron species (Fe@HTC and Fe@HTC−T) were prepared by chemical co-precipitation and tubular furnace sintering treatment to develop efficient and sustainable catalysts for antibiotic wastewater treatment, addressing key challenges in sustainable environmental management. The characterization results indicated that iron species loaded on the hydrochars changed from Fe₃O₄ to FeO and then to metallic Fe with the pyrolysis temperature increased from 400 °C to 800 °C. The results of the characterization revealed a phase transition of iron species, confirming the temperature-dependent evolution of catalytic activity. The catalytic performance of the hydrochar composites was evaluated for tetracycline hydrochloride (TC–HCl) degradation via a Fenton-like process. Under optimal conditions (0.2 g/L TC–HCl, 0.1 g/L catalyst, 0.1 mM H₂O₂, pH = 6.86), Fe@HTC−T demonstrated excellent catalytic activity with a removal efficiency of 91.2%. Moreover, Fe@HTC−T exhibited superior stability and low iron leaching rates, attributed to the protective role of the hydrochar matrix. Mechanism research suggested that hydroxyl radicals (•OH) played a dominant role in the degradation process. This study demonstrates the potential of utilizing low-cost and renewable hydrochar materials derived from biomass waste to address industrial challenges in treating high-concentration antibiotic wastewater, offering a sustainable and cost-effective solution with broad applications in environmental remediation. Full article

Non-noble metal electrocatalysts for the hydrogen oxidation reaction (HOR) that are both highly active and low-cost are essential for the widespread use of fuel cells. Herein, a simple two-step method for creating an in-plane heterostructure of Ni₃N/MoSe₂ loaded on N-doped reduced graphene oxide (Ni₃N/MoSe₂@N-rGO) as an effective electrocatalyst for the HOR is described. The process involves hydrothermal treatment of the Ni and Mo precursors with N-doped reduced graphene oxide, followed by the annealing with urea. The Ni₃N/MoSe₂@N-rGO catalyst exhibits high activities for the HOR, with current densities of 2.15 and 3.06 mA cm⁻² at 0.5 V vs. the reversible hydrogen electrode (RHE) in H₂-saturated 0.1 M KOH and 0.1 M HClO₄ electrolytes, respectively, which is comparable to a commercial 20% Pt/C catalyst under similar experimental conditions. Furthermore, the catalyst demonstrates excellent durability, maintaining its performance during accelerated degradation tests for 5000 cycles. This work offers a practical framework for the designing and preparing of non-precious metal electrocatalysts for the HOR in fuel cells. Full article

A UO₂²⁺ complex bearing N, N, N′, N′-tetraisopropyldiglycolamide (TiPDGA) and two DMF molecules was prepared to explore the catalytic activities of the Lewis-acidic U centre. The cationic complex, [UO₂(TiPDGA)(DMF)₂]²⁺, was obtained as a ClO₄⁻ salt under optimised reaction conditions with an appropriate mixing ratio between UO₂²⁺ and TiPDGA to maintain 1:1 stoichiometry, a non-coordinating ClO₄⁻ counteranion to reserve the coordination sites for substrate activation, and the presence of extra HClO₄ to suppress undesired hydrolysis of UO₂²⁺ competing with the expected complex formation. This UO₂²⁺ complex was characterised by IR, elemental analysis, X-ray crystallography, and ¹H NMR to confirm that the desired [3+1+1] equatorial coordination is actually formed in the solid state and is still maintained even after dissolution in CD₂Cl₂. [UO₂(TiPDGA)(DMF)₂]²⁺ was further subjected to nucleophilic acyl substitution reactions of acid anhydrides to assess its activity and capability as a Lewis-acid catalyst there. Although the observed reaction rates were not very rapid, some characteristic aspects to gain reaction- and substrate-selectivity appeared thanks to the equatorial coordination sphere sterically regulated by the tridentate auxiliary TiPDGA ligand and labile monodentate DMF molecules to activate an acid anhydride after ligand substitution. Full article

In this study, biochar-loaded E³⁺:BiOCl (C/3E³⁺:BiOCl) was synthesized with varying levels of E³⁺ doping using a one-step solvothermal method and used for tetracycline hydrochloride (TC-HCl) degradation. Their structure, shape and morphology were not only characterized by power X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) but also by UV-vis diffuse reflectance spectra and upconversion (UC). The results indicated a significant enhancement in the photocatalytic activity of the catalyst following the introduction of Er³⁺. The composite material C/3E³⁺:BiOCl, with a doping concentration of 3 mol%, demonstrated the highest photocatalytic activity, achieving an impressive visible light degradation efficiency of 89.2% for TC HCl within 90 min. This marks an increase of 33.5% compared to the BiOCl monomer and 17.4% compared to C/BiOCl. Additionally, when exposed to light with wavelengths exceeding 600 nm, C/3E³⁺:BiOCl maintained a photodegradation efficiency of 44.3%, while BiOCl and C/BiOCl showed no photocatalytic activity under the same conditions. This finding highlights the effectiveness of BiOCl as a doping matrix, which enhances the photocatalytic performance of BiOCl through the upconversion effect of E³⁺ and the electron transfer mechanisms associated with biochar. Full article