The conversion of CO2 from biomass-derived streams into synthetic methane is a promising carbon capture and utilization (CCU) pathway. In this work, agricultural residues-pistachio (PS), almond (AS), and nut shells (NS)-are valorized into steam-activated biochars that serve as supports for Ni-based methanation catalysts. Steam activation yielded microporous PS biochar, while AS and NS produce mesoporous biochars After impregnation with 10 wt% Ni XRD of reduced samples reveals Ni0 and Ni2+ in 10Ni-AS and 10Ni-NS, whereas 10Ni-PS is fully reduced to metallic Ni. XPS identified sp3-hybridized carbon species and C–N bonds in 10Ni-PS, indicating nitrogen functionalities that enhance CO2 adsorption; this catalyst achieves XCO2 = 23% and SCH4 = 64% at 400 °C. Additionally, the effects of PS activation temperature are examined, higher Ni loading (15 wt%), and Mg incorporation as a secondary metal. Higher Ni loadings and lower activation temperatures diminish performance. Conversely, 10Ni-1Mg-PS reach XCO2 = 52.7% and SCH4 = 81.3% at 400 °C. Magnesium increases basic site density, promotes CO2 adsorption/activation, and improves thermal stability and coke resistance. A 190 h continuous-flow test at 400 °C with 10Ni-1Mg-PS reveal deactivation due to Ni leaching into the aqueous phase. Overall, steam-activated pistachio biochar emerges as an efficient, cost-effective support for Ni/Mg catalysts in CO2 methanation, with performance governed by support porosity, surface N functionalities, promoter-induced basicity, and control of Ni leaching under continuous operation. These findings contribute to the development of renewable, waste-derived functional materials for integrated CO2 capture and utilization processes.
The dependence on conventional fossil fuels for energy generation and the constant combustion of carbonaceous fuels have led to significant environmental stress. To address this issue, chemical looping technology is on the rise due to the controlled oxidation of fuel via a sustained redox reaction between the fuel and the carrier more advantages compared with other traditional technologies. This review highlights the oxidation of various waste biomass in a typical chemical looping gasification setup. The nature of the waste biomass and the type of oxygen carrier used can significantly influence hydrogen production during chemical looping gasification. On average, more than 80% of biomass can be converted using agricultural biomass, whereas wood waste biomass shows a higher conversion rate (>90%). This review also provides valuable insights into modifications of oxygen carriers with other compounds, such as calcium oxide, which acts as a sorbent to capture flue gas and increase the carrier's interaction with the fuel for enhanced syngas generation. A brief discussion of the roles of machine learning models and deep learning networks in optimizing chemical looping gasification is presented. Overall, waste biomass can be effectively utilized in a chemical looping system, thereby replacing fossil fuels in conventional chemical looping combustion.
The environmental impact of anthropogenic pollution has driven the search for efficient photocatalysts. Fe-decorated TiO2 nanostructures were synthesized via hydrothermal method at controlled pH values (6, 8, and 10) followed by Fe impregnation (0.2 – 1.6 wt%), and evaluated for dye degradation and CO2 photoreduction. XRD, Raman, and XPS confirmed anatase retention and atomically dispersed surface Fe3 + species. Increasing Fe content decreased dye degradation but enhanced CO2 photoreduction, showing an opposite trend explained by a unified Fe3+/Fe2+ redox-trap mechanism: Fe3+ captures electrons, prolonging charge separation; excess Fe2+ scavenges holes, suppressing dye radicals while accumulating electrons for CO2 reduction. Thermal treatment (400 °C for 4 h) improved performance in the pH 6 and 8 samples but not in the pH 10 sample or commercial TiO2. Samples prepared at pH 8 showed the best CO2 photoreduction, attributed to a facet-driven surface heterojunction acting synergistically with Fe species. These findings establish design principles for tuning TiO2 photocatalysts toward selective oxidation or reduction applications.
Antidepressant pollution is an emerging environmental threat. Citalopram (CIT) is one of the most prescribed drugs for anxiety and depression. It saves lives. However, the global consumption of CIT leads to its environmental persistence. In this study, we present the first high-efficiency solar-active photocatalyst designed for the degradation of CIT: a nickel-cobaltite@reduced graphene oxide nanocomposite (NC@rGO). Detailed characterization techniques (TEM, SEM, XRD, Raman/IR spectroscopy, BET, zeta potential, and electrochemistry) reveal that the material consists of approximately 20 nm NC particles supported on conductive rGO sheets, featuring a surface area of 33 m2 g−1 and stable dispersion in aqueous solutions across various pH levels. This synergistic structure facilitates remarkable solar photocatalytic performance, achieving 73% CIT degradation within 120 min under solar light. Mott-Schottky analysis and scavenger studies confirm that degradation proceeds via direct hole oxidation and •O₂- radical attack. Critically, LC-MS/MS identification of degradation intermediates and subsequent cytotoxicity assays confirm that the process eliminates the parent pollutant without generating harmful byproducts. The NC@rGO composite thus offers a potent, environmentally benign solution for mitigating antidepressant pollution.
Metal sulfides (MSs) exemplify a pivotal category of materials for solar light driven photocatalysis owing to their broad range of light absorption capacity, supreme negative conduction band potential and tunable electronic properties across binary, ternary, and quaternary systems. In addition, surface plasmonic resonance and photothermal properties of few selected MSs stimulate their catalytic properties spanning the NIR region. As the single phase semiconductors exhibit poor efficiency, heterojunction with MSs has acquired enormous interests due to the synergism in the charge carrier separation proficiency and enhanced optical properties. In this regard, S-scheme heterojunction (SSH) have recently transpired as an advanced charge transfer strategy that is capable of resolving the persistent conflict between the efficient charge separation and strong redox capability. This review bestows a systematic and holistic outline of MS-SSH, beginning with tentative classification of MSs as OP and RP based on their band edge positions. It further examines the fabrication strategies of MS-SSH such as self-assembly, solvent evaporation, in-situ growth and interfacial sulfidation, and co-precipitation, with emphasis on MOF/COF-derived architectures and co-cationic heterojunctions. The key design principles consisting of band-gap responses, interfacial engineering, defect engineering, hierarchical architectures (0D-3D), and dual SSH are critically discussed. The photocatalytic performance of MS-SSH towards H2 evolution, CO2 reduction, pollutant degradation and heavy metal reduction, nitrogen fixation and H2O2 synthesis are underscored. Finally, the unresolved challenges including photocorrosion, uncertainties in validating the S-scheme charge-transfer mechanisms, and future direction of the research are proposed.
Ammonia catalytic combustion technology enables the efficient conversion of NH3 into nitrogen (N2) and water (H2O), offering a reliable carbon-free fuel utilization strategy. This approach effectively addresses the inherent challenges associated with NH3 combustion, including high ignition temperatures, low N2 yields, and combustion instability. This study focuses on the catalytic process characteristics and mechanism of NH3 combustion over spherical CeO2-supported transition metal catalysts. Cu/CeO2, Mn/CeO2, and Ni/CeO2 catalysts were synthesized by impregnation method. The catalytic performance for NH3 combustion revealed a clear activity trend of Mn/CeO2 > Cu/CeO2 > Ni/CeO2. However, the most active catalyst, Mn/CeO2, also showed the least N2 yield. In contrast, Cu/CeO2 emerged as the balanced performer, coupling high NH3 conversion (~100%) with good N2 yield (88.7%–90.4%) over 10 hours, and achieving self-sustained combustion at 7.1% NH3. Mechanistic studies attribute Mn/CeO2’s high activity to a synergistic interplay where Ce4+ oxidizes Mn2+ to Mn3+, stabilizing more oxygen vacancies, which confirmed by Density Functional Theory (DFT) calculation. The low N2 yield of Mn/CeO2 is linked to its inferior reduction ability and diminished NH3 adsorption capacity, as revealed by H2 temperature-programmed reduction (H2-TPR) and temperature-programmed desorption of NH3 (NH3-TPD-MS). In-situ infrared transmission spectroscopy (IR) results found that the adsorbed NHx can react with HNO species in Mars-van-Krevelen (M-K) mechanism over Cu/CeO2 catalyst. And a rapid consumption of NOx indicates an intensive internal selective catalytic reduction (i-SCR) pathway, which effectively accounts for the high N2 yield observed in Cu/CeO2. But the Mn/CeO2 exhibited weaker HNO formation and lower i-SCR activity, in consistent with its inferior N2 yield. These results provide a guidance for the design of advanced catalysts and promote insight into the mechanistic pathways of ammonia catalytic combustion.
Developing noble-metal-free photocatalysts for selective solar-driven C–N heterocycle synthesis remains a key challnage in sustainable organic chemistry. Herein, C, N, and S-modified anatase/brookite TiO2 was prepared through a thiourea-assisted post-treatment and used for the one-pot synthesis of 2-methylbenzimidazole under simulated sunlight. The non-metal modification enhances visible-light response by narrowing the band gap and generating defect-related electronic states. Under simulated solar light, the optimized CNS-TiO2 achieved complete o-dinitrobenzene conversion with 92% yield and selectivity toward 2-methylbenzimidazole, outperforming both undoped TiO2 and commercial Au-loaded TiO2. Surface acid-site analysis, together with p-toluenesulfonic acid-assisted experiments, confirmed that Brønsted acidity strongly promotes the condensation/cyclization steps, raising the yield to 99%. Mechanistic studies based on substrate/donor screening and intermediate detection suggest a coupled photo-redox and acid-assisted pathway involving nitro reduction, alcohol oxidation, C–C bond cleavage, and heterocycle formation. This work highlights a solar-driven strategy for transforming nitroarenes into valuable benzimidazoles using a multifunctional donor and a cocatalyst-free TiO2 platform.
Ni-based catalysts are widely investigated for dry reforming of methane (DRM) but often suffer from rapid deactivation caused by sintering and oxidation under high-temperature conditions. In this study, NiMo bimetallic catalysts supported on dealuminated mesoporous beta zeolite (DBeta) were synthesized via a vapor-phase metal diffusion method to stabilize Ni nanoparticles within defect-rich zeolite frameworks. Dealumination of the beta zeolite generated silanol nest defects that serve as anchoring sites for metal species, enabling defect-selective metal trapping during vapor-phase synthesis. As a result, highly dispersed Ni–Mo nanoparticles were confined within the porous structure of DBeta. Under DRM conditions, Mo species dynamically transformed into Mo2C, which promoted CO2 activation and mitigated Ni oxidation through a redox cycle. The optimized NiMo0.2/DBeta catalyst exhibited excellent stability, maintaining CH4 and CO2 conversions of 71.0% and 78.3%, respectively, for 100h at 750°C under a WHSV of 120L gcat−1 h−1. The enhanced catalytic stability arises from the synergistic effect of defect-mediated metal confinement and dynamic Mo2C formation. This work establishes a defect-directed metal trapping strategy that integrates zeolite defect engineering with dynamic carbide promoters, providing a general design principle for stabilizing transition-metal catalysts under harsh reforming conditions.
Valorization of invasive weeds offers a sustainable pathway for environmental remediation. Herein, a tungsten trioxide nanoparticles-supported magnetic nanobiochar catalyst was synthesized from Parthenium hysterophorus a biomass for azo dye removal. Advanced spectroscopic analyses confirmed that the catalyst possesses an optimal band gap of 3.27eV, a high electroactive surface area of 0.00114mA/cm2, and improved charge-transfer characteristics. The catalyst showed high photocatalytic activity, achieving 94.45% Congo Red (CR) degradation at pH 3 (20mg/L catalyst, 120min UV) following pseudo-first-order kinetics and exhibiting higher selectivity towards CR than Rhodamine B (76.24%) and Eosin Y (64.92%). Under simulated wastewater conditions, the catalyst maintained consistent activity in the presence of inorganic ions and humic acid, with ROS trapping confirming superoxide and hydroxyl radicals as the main active species, and maintained 92.61% of efficiency after five cycles, demonstrating high stability and reusability. The suggested mechanism and catalyst's mineralization capacity were validated by GC-MS analysis, which also verified the creation of smaller fragments following CR breakdown. Overall, our work demonstrated the successful conversion of an invasive weed into a high-performance nanobiochar-based catalyst, offering a practical and economical solution that addresses solid waste valorization and effective wastewater treatment at the same time.
The development of highly efficient and recyclable heterogeneous catalysts for the reduction of hazardous organic pollutants continues to be a significant problem in environmental remediation. In this regard, three-dimensional framework carbon (3DFC) as support material was prepared using calcination of sodium citrate for the immobilization of palladium nanoparticles (3.90± 0.80nm) (PdNPs-3DFC). The PdNPs-3DFC catalyst was characterized with various advanced characterization techniques. Consequently, the PdNPs-3DFC catalyst exhibited excellent catalytic activity toward the reduction of various nitrophenols, and organic dyes including 4-nitrophenol (4-NP), 3-nitrophenol (3-NP), 2-nitrophenol (2-NP), 2,4-dinitrophenol (2,4-DNP), 2-chloro-4-nitrophenol (2-CNP), methyl orange (MO) and rhodamine B (RhB). The catalytic activity was eventually retained after five recycles for the reduction of pollutants (4-NP, RhB and MO), confirming the excellent stability of the PdNPs-3DFC catalyst. The proposed catalyst revealed the excellent catalytic efficiency for the simultaneous removal of multiple pollutants (4-NP, RhB, and MO) system with conversion rate of > 98 % within 12min. The catalyst was loaded into the fixed bed system for 4-NP removal in a continuous flow system with the retention of efficiency more than 99% and its long-term stability. These results demonstrate that the integration of PdNPs with 3DFC support creates a beneficial structure-property relationship that improves the catalytic performance and stability, underscoring the potential of PdNPs-3DFC as an effective catalyst for continuous wastewater remediation.
