Hydrogen-bonded organic frameworks (HOFs) are an emerging class of crystalline porous materials assembled through intermolecular hydrogen-bonding interactions between organic building units. Distinguished from metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), HOFs are entirely metal-free, exhibit excellent solution processability, and can be regenerated through simple recrystallization, making them highly attractive for sustainable environmental applications. This review systematically surveys the environmental applications of HOFs, encompassing (i) selective gas adsorption and separation of industrially relevant gas pairs (C2H2/CO2, C2H6/C2H4, CH4/C2Hx, Xe/Kr, NH3), (ii) CO2 capture, sensing, and photocatalytic reduction, (iii) proton conduction for clean energy fuel cells, (iv) photocatalytic hydrogen evolution via band-gap-engineered is reticular HOFs, (v) enzyme encapsulation for biocatalytic remediation of toxic organophosphorus compounds, (vi) luminescence- and electrochemical-based sensing of heavy metal ions and antibiotic contaminants, (vii) oil/water separation using superhydrophobic metal-mediated HOFs, and (viii) antimicrobial membranes exploiting ionic HOF architectures. The interplay between molecular design, pore chemistry, and environmental performance is critically analyzed, and key challenges including scalability, long-term water stability, and mechanistic understanding are discussed alongside future research directions.
Grafting molecular Cr–PNP complexes onto the amino groups of metal–organic frameworks (MOFs) constitutes a promising strategy for anchoring selective ethylene oligomerization catalysts on a crystalline, porous support; however, a conflict exists between high amino density and framework porosity. Herein, we employ a mixed-ligand approach in which 2-amino-1,4-benzenedicarboxylic acid and terephthalic acid were combined at four molar ratios to construct two large-pore frameworks with tunable amino content, UiO-66 and MIL-101(Cr) (denoted MixNU and MixNM). The amino groups were phosphinated with chlorodiphenylphosphine and subsequently metalated with Cr(III) to afford the grafted catalysts MixNUPCr and MixNMPCr. Multiple characterization techniques confirmed that the framework structure and crystallite morphology were preserved throughout phosphination and metalation. Pre-formed Cr–PNP sites exhibited markedly higher catalytic activity than chromium generated in situ or introduced by impregnation, and produced no polyethylene. Activity varied with amino content and peaked at an amino/terephthalate molar ratio of 2:3: MixNUPCr-2 reached 2.49 × 105 g·mol−1·h−1 with a C6 + C8 selectivity of 71.14%, while MixNMPCr-2 reached 1.01 × 105 g·mol−1·h−1 with a C6 + C8 selectivity of 62.07%. MixNUPCr-2 retained 82% of its peak activity at 60 °C and exhibited no appreciable loss of activity or crystallinity over four cycles. Density functional theory calculations reproduced the metallacycle mechanism and confirmed that ring expansion of the chromacyclopentane intermediate is favored over 1-butene release, consistent with the C6/C8-rich product distribution observed experimentally.
Two-dimensional (2D) materials have attracted significant attention as advanced photoelectrocatalysts for environmental remediation and sustainable hydrogen production. This review critically discusses recent advances in various 2D layered materials, including MXenes, graphene and its derivatives, hexagonal boron nitride (h-BN), layered double hydroxides (LDHs), graphitic carbon nitride (g-C3N4), and metal chalcogenides-based materials in photoelectrocatalytic degradation of pharmaceuticals and personal care products (PPCPs) and solar-driven hydrogen (H2) production. The preparation methods governing the surface, electronic, structural and optical properties have been discussed, highlighting their influence on photoelectrocatalytic activity. The fundamental principles of photoelectrocatalysis are also examined, including light absorption, electron-hole pair generation, charge-carrier separation, interfacial charge transfer, reactive oxygen species formation, and surface redox reactions. Furthermore, the application of 2D materials in photoelectrocatalytic removal of pharmaceuticals in terms of reaction mechanisms and kinetics are discussed in detail. In addition, H2 production using 2D material-based composites, along with the associated mechanistic pathways and kinetic parameters, has been comprehensively analyzed. Despite these advances, several challenges remain, including incomplete mechanistic understanding, nanosheet restacking, defect control, photocorrosion, catalyst leaching, long-term stability, real-wastewater performance, and scalable electrode fabrication. Thus, this review not only consolidates existing knowledge but also explores key research directions to address these challenges associated with both photoelectrocatalysis and 2D material-based composites.
In this study, the electrogeneration capacity of hydrogen peroxide (H2O2) was evaluated using an unmodified Printex L6 carbon-based gas diffusion electrode (GDE) and a GDE modified with SnO2 and Nb2O5 (GDE-m). The GDE-m exhibited superior performance, achieving ∼1.2-fold higher accumulated H2O2 concentrations under all tested conditions. Subsequently, the GDE-m was applied in different electrochemical advanced oxidation processes for the degradation of bisphenol F (BPF): anodic oxidation with electrogenerated H2O2 (e-H2O2), and UVC-activated e-H2O2 (UVC/e-H2O2), at three current densities (50, 75, and 100 mA cm−2). Isolated processes (photolysis and anodic oxidation) achieved limited removal efficiency (< 25%), while e-H2O2 reached up to 78% abatement at 100 mA cm−2 after 90 min. The UVC/e-H2O2 process showed superior performance, with 86% removal at 50 mA cm−2 and complete BPF elimination within 30 min (75 mA cm−2) and 15 min (100 mA cm−2). Finally, the UVC/e-H2O2 process was evaluated in different aqueous matrices: deionized water (DI), tap water (TW), and lake water (LW). In TW, the fastest BPF degradation was observed, (100% in 45 min at 50 and 75 mA cm−2), likely due to the combined influence of dissolved inorganic species, alkalinity, and pH, which may affect reactive oxidant generation and stability. In contrast, DI showed lower mineralization efficiency, while LW exhibited poorer performance (77.4% at 50 mA cm−2 after 90 min). These results highlight UVC/e-H2O2 as a promising alternative for rapid BPF abatement, while also indicating that mineralization efficiency and by-product formation must be considered when applying the process to complex water matrices.
The present study reports the synthesis of polyol esters from trimethylolpropane (TMP) and fatty acids via an esterification process catalyzed by a series of mixed-linker sulfonic acid-functionalized UiO-66 catalysts with varying sulfonic ligand ratios. A comprehensive structural analysis revealed the successful attachment of sulfonic acid groups (–SO3H) to the UiO-66 framework while preserving its characteristic topology. An increase in sulfonic ligand content progressively enhanced the total acidity from 1.67 to 3.71 mmol g−1, but resulted in a decline in crystallinity and surface area. The UiO-66 containing 40 mol% of the sulfonic acid-containing benzenedicarboxylate linker exhibited the highest catalytic activity. This optimal performance was attributed to the best balance achieved between Brønsted acid site density and Lewis acid site accessibility at this intermediate ligand ratio, enabling effective Brønsted-Lewis acid synergy under pore-diffusion conditions. Furthermore, the catalyst demonstrated excellent reusability over multiple cycles. The present work elucidates the influence of sulfonic ligand ratio on the structure and catalytic performance of UiO-66, providing a robust heterogeneous catalyst for the green synthesis of polyol esters.
The sustainable valorization of agricultural waste into high-performance catalytic materials represents a critical pathway toward the circular economy and renewable energy production. Herein, we report a one-pot hydro-thermal synthesis of c-axis-oriented sheet-like ZSM-5 zeolites (S-ZSM-5) using silicalite-1 seeds and rice husk (RH)-derived amorphous silica as a renewable and environmentally benign sole silicon source, without expensive organic structure-directing agents or additional growth-directing additives. The slow dissolution of solid amorphous silica, in synergy with seed-induced nucleation, created an anisotropic growth environment consistent with the competitive growth model, directing preferential crystal growth along the c-axis and led to intergrown S-ZSM-5 nanosheets with intercrystalline mesopores. The seed-to-silica molar ratio served as a key parameter for tuning the hierarchical pore structure of the resulting S-ZSM-5 zeolites. The optimized S-ZSM-5-0.2 catalyst exhibited a high BET surface area of 346 m2 center dot g-1, a mesopore volume of 0.09 cm3 center dot g-1, and abundant strong acid sites. In the catalytic fast pyrolysis (CFP) of corn stalk, S-ZSM-5-0.2 achieved a maximum benzene, toluene, and xylene (BTX) yield of 91.68 mg center dot g-1, representing a 21% enhancement over conventional ZSM-5 synthesized from TEOS (75.84 mg center dot g-1). The c-axis-oriented short straight channels of this material significantly enhanced molecular diffusion and mass transfer, promoting deoxygenation and aromatization reactions while effectively suppressing coke formation (as confirmed by a reduction in coke deposition from 13.15 wt% to 10.81 wt%). This work provides a straightforward and scalable strategy for economical converting agricultural waste into hierarchical zeolites with a tailored crystal orientation, offering a promising and sustainable route for biomass-to-aromatics conversion and advancing the development of waste-derived catalysts for green chemistry applications.
EDTA-enhanced Co and Ni extraction from low-grade ultramafic ore deposits can be promising if coupled to a concentration process for those elements. This study evaluates the efficiency of autocatalysis and decomplexation of metal-EDTA chelates using peroxymonosulfate (PMS) followed by recovery as sulfide minerals. At a relatively low PMS:EDTA ratio of 4 and low pH (1.9-2.1), both Co and Ni autocatalyzed the decarboxylation of 46% of EDTA, but at different rates (1 h for Co; 7 days for Ni). At these conditions, changes in the UV-Vis spectra of Co solutions are consistent with formation of a stable Co(III) complex, while approximately 10% of Ni remains a stable Ni-EDTA complex, preventing complete precipitation. Sulfide addition doubles the efficiency of Ni recovery (73%) but does not improve the Co recovery (35%) relative to the traditional NaOH method. Recovery yields are increased to 100% for Ni and 55% for Co at a PMS:EDTA ratio of 16 using sulfide addition. Addition of 10-25% Co to either Ni or Fe did not significantly increase the rate of decarboxylation of EDTA, however recovery of Co during sulfidation is more strongly and positively affected by metal mixtures than either Ni or Fe, resulting in higher yield. Further, it seems the presence of Ni has a much larger effect on Co precipitation than expected based on the amount of decarboxylation.
Through co-precipitation, and surfactant and urea-assisted hydrothermal syntheses, V, Ti or Ce were tentatively introduced in CuCo-based layered double hydroxides (LDH) to control the morphology, electronic properties, and porosity of their derived layered double oxides (LDO). The solids were characterized by X-ray diffraction (XRD), textural properties, Raman and Fourier transform infrared (FTIR) spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM-EDS) and Electron paramagnetic resonance (EPR) measurements. Variations in the type of third metal incorporation using the two synthesis methods resulted in distinct metal valences, lattice defects and surface chemistry properties playing a pivotal role in the glycerol valorization reactions. The structures and oxygen vacancy-mediated ternary synergy in CuCo-based oxides derived from layered double hydroxides are deeply investigated. A promising synthetic route to obtain CuCoCe catalyst for acetalization of glycerol with furfuraldehyde as substrate resulted in glycerol conversion of 78% and selectivity to the 5- and 6-membered acetals of 20%. The presence of CuCo2O4 phase and oxygen vacancy-mediated ternary synergism owing to the Ce presence in the oxides resulted in better catalytic properties towards glycerol valorization to produce cyclic acetals.
The unique catalytic performance of sulfide-modified Pd is largely attributed to its enhanced selectivity for nitro hydrogenation versus dechlorination. However, the microscopic mechanism for such a high selectivity remains unclear. In this work we investigated the ligand adsorption behavior on the surfaces of a sulfided Pd using both chemical adsorption equilibrium model calculated from the CO chemisorption data and density functional theory calculation. The chemical adsorption data reveal preferential site occupation of sulfide ligands at most active Pd surface sites. There exist three types of Pd sites with varying catalytic activity, that is, corner, edge and terrace sites. For the sulfide-modified surface, the most active Pd corner sites preferentially bind sulfide ligand, followed by the less active Pd edge sites. Then only the least active Pd terrace sites are left exposed. Further kinetic measurements and the binding energy calculations reveal that dechlorination requires a significantly higher activation energy than nitro‑hydrogenation. The exposed less active terrace sites can only generate a weakly activated hydrogen, which is sufficient to reduce the nitro group but insufficient to break the C-Cl bond. The high selectivity due to a high preference in site occupation by sulfide ligands fundamentally suppresses the dechlorinating side reaction. The insights provided in this work not only unravels the quantitative understanding of surface coordination chemistry, but also makes this material design an unambiguous strategy in searching highly selective metal catalysts.
Interactions between Fe-Ni-S cluster and amino acid play an essential role in the efficient carbon dioxide (CO2) reduction reaction catalyzed by [NiFe]‑carbon monoxide dehydrogenase (CODH), one of the ancient CO2 reductases. Because of the structural similarity to the active core of CODH, the violarite (FeNi2S4) mineral has been postulated as the inorganic origin of CODH. However, how the mineral core could have been functionalized by the interaction with amino acids remains largely elusive. Here, we report that the selectivity of CO2 reduction by violarite at −0.87 V vs. reversible hydrogen electrode (RHE) is markedly influenced by the functional groups of amino acids. Bare violarite catalyzes CO2 reduction to form carbon monoxide and methane, while the coordination with histidine directs the reaction pathway for formate synthesis. Vibrational spectroscopic analysis using histamine and glycine as alternative amine compounds shows that the imidazole group coordinates directly with CO2 and acts as a cofactor in CO2 reduction, similar to the enzymatic reaction in CODH. Our study provides the first insight into the influence of amino acids on the CO2 reduction by metal sulfide minerals. This, in turn, sheds light on the origin of life model at deep-sea hydrothermal vents, where metal sulfides are predicted to have functioned as proto-enzymes for the carbon fixation reaction.
Hydrochloric acid digested carbon - manganese oxide black powder and partially degraded zinc container material from spent Zn-C battery cells were used to prepare a low-cost ZnMnOx/C catalyst. This material exhibited excellent catalytic performance for the hydrogenation of levulinic acid, yielding a mixture of gamma-valerolactone (GVL) and valeric acid anhydride (VAA). The Zn and Mn contents of the ZnMnOx/C catalyst were determined to be 36 +/- 1 and 29 +/- 1 wt%, respectively. The complete 100% levulinic acid conversion was achieved under optimized conditions: 13.3 g of ZnMnOx/C catalyst per mol of levulinic acid, 5.17 MPa H2, 190 degrees C, and an 8 h reaction time; producing a GVL: VAA product ratio of 12: 88. The proportion of valeric acid anhydride increased with increasing reaction temperature, with the highest selectivity again observed at 190 degrees C after 8 h under 5.17 MPa H2. Catalyst recyclability tests showed a gradual decline in activity, with levulinic acid conversion decreasing from 100% to 75% after four consecutive reaction cycles.
Bulk ZrO2-based materials have become a new class of alkane dehydrogenation catalysts performing superior to catalysts with supported metal or metal oxide species. The nature of active sites and the mechanism of propane dehydrogenation over these materials have been elucidated, while coke formation is not well understood. To close this gap, we applied time-resolved operando UV–vis spectroscopy for analyzing coke formation/removal over ZrO2, LaZrOx, YZrOx and Rh/YZrOx in propane dehydrogenation under industrially relevant conditions. Such analysis was complemented by temperature-programmed oxidation of spent catalysts. A consecutive mechanism of coke formation was suggested. Propene initially forms low-condensed hydrocarbons followed by their conversion into polyaromatics finally giving graphitic-like deposits. The rate of these steps depends on the kind of promoter for ZrO2 and Rh presence.
The catalytic efficacy of supported metal catalysts is inextricably linked to their structural characteristics. Although transition metal catalysts are extensively utilized across diverse catalytic reactions owing to their pronounced activity, they are frequently susceptible to metal leaching and deactivation in liquid-phase environments, concomitant with challenges in regeneration. The strong metal-support interaction (SMSI) presents a viable approach to bolster the stability of supported metal nanoparticles; however, this often comes at the expense of diminished activity, primarily attributable to either the encapsulation of active sites by the support or an excessively robust metal-support linkage. In this investigation, we rationally designed a supported transition metal nano catalyst by integrating transition metal ions into a hydroxyapatite (HAP) matrix to modulate the SMSI. The resultant catalyst demonstrates exceptional catalytic activity coupled with remarkable stability, exhibiting negligible transition metal leaching during Fenton-like degradation processes. Comprehensive characterization elucidates that the incorporation of transition metals into the HAP lattice reinforces the metal-support interaction, thereby effectively anchoring the transition species. Furthermore, the ion-exchange synthetic protocol confers an augmented specific surface area of the active metal component, consequently endowing the supported transition nanoparticles with both heightened catalytic activity and enhanced stability.
The thermocatalytic conversion of CO2 into high-value chemicals such as methanol offers a promising route to mitigate greenhouse gas emissions, driving the need for highly efficient and stable catalysts. In this work, we overcome the typical activity–selectivity trade-off in methanol synthesis by incorporating La into a Cu-based catalytic system. Detailed characterization shows that La doping induces electron enrichment of ZnOX even before reduction, which suppresses electron transfer from Cu to ZnOX during reduction and thereby increases the proportion of active Cu0 sites for CO2 hydrogenation. Through combined spectroscopic analysis and DFT calculations, we propose a dual-site mechanism involving Cu0-ZnOX and Cu0-La2(CO3)3 interfaces, where the migration of HCOO* between these sites is key to enhancing both catalytic activity and selectivity. The optimized La-modified catalyst achieves 63.23% CO2 conversion and 85.32% methanol selectivity. This work demonstrates a rational strategy for designing high-performance CO2-to-methanol catalysts via electronic modulation and interface engineering.
The increasing global demand for clean water and sustainable energy is driving intensive research into advanced materials for water remediation and clean energy production. Herein, different concentrations of Ti_Bi2O3 were synthesized at 25% Ti_ Bi2O3, 50% Ti_ Bi2O3 and 75% Ti_ Bi2O3 using hydrothermal method. The influence of varying Ti concentration on the structural, morphological, photocatalytic and electrocatalytic properties was investigated. X-ray Diffraction (XRD) confirmed the monoclinic phase of Bi2O3 and showed successful Ti incorporation which caused peak broadening and shifts. Fourier-transform Infrared Spectroscopy (FTIR) proved the formation of Ti-O-Bi bonds showing effective doping. SEM analysis revealed both spherical shaped and needle shaped structures and for 75% Ti_ Bi2O3 the average particle size was found to be 98.06 nm. Photocatalytic activity was measured using Congo red dye degradation under UV light which showed as Ti doping increased the photocatalytic degradation % increased and reached 98.71% degradation at 50% Ti concentration. Electrocatalytic activity measured using LSV and CV showed 75% Ti_Bi2O3 has the best OER and HER catalytic performance with OER Tafel slope of 221.31 mVdec- 1. Cyclic voltammetry (CV) data also supports 75% Ti_Bi2O3 nanoparticles having the highest electrocatalytic activity with the highest overall capacitive current response.
Photocatalytic processes are widely used as sustainable technologies for environmental remediation and energy-related applications. However, the efficiency of semiconductor photocatalysts is limited by electron-hole pair recombination and by insufficient compression of the semiconductor's electronic transport mechanisms under illumination. Electrochemistry provides tools to elucidate and control these processes. Although electrochemistry is frequently used for characterization purposes, its broader role in photocatalytic systems remains underappreciated. This review focuses on promoting electrochemistry not only as a characterization technique but also as a mechanistic platform, encompassing the synthesis of photocatalytic materials, the evaluation of charge-separation efficiency, electronic transport properties, and recombination phenomena under illumination. This collective knowledge drives the degradation of pollutants through mineralization. In this regard, this work first reviews electrochemical alternatives for the synthesis of photocatalysts, highlighting the advantages of the resulting materials. Next, the role of electrochemical techniques, such as cyclic and linear sweep voltammetry, chronoamperometry, electrochemical impedance, and photocurrent measurements, in the characterization and understanding of photocatalytic phenomena is examined. The integration of electrochemistry and photocatalysis in photoelectrocatalysis is analyzed, highlighting its ability to reduce recombination and thereby improve the mineralization efficiency of pollutants. Thus, applications in the degradation of pollutants are discussed, emerging concepts such as biophotoelectrocatalysis and energy generation are introduced, from which it is possible to position electrochemistry as a powerful tool to promote and complement the advancement of next-generation photocatalytic technologies.
Calcium and nitrogen co-doped titanium dioxide (Ca-TiO2@N) photocatalyst was successfully synthesized via a two-step wet impregnation-hydrothermal method to enhance photocatalytic degradation of methylene blue (MB) under UV-Vis irradiation. Structural, morphological, and optical characterizations using XRD, SEM, EDX, FTIR, and diffuse reflectance spectroscopy confirmed successful incorporation of Ca and N into the TiO2 lattice without altering the anatase phase, while promoting reduced particle size, increased surface porosity, and bandgap narrowing. The synergistic effect of Ca and N co-doping improved visible-light absorption, enhanced charge separation, and suppressed electron-hole recombination, leading to greater reactive oxygen species generation. Under optimal conditions, Ca-TiO2@N achieved 87.48% MB degradation and 67.92% total organic carbon removal within 180 min, following pseudo-first-order kinetics with a rate constant of 0.0114 min-1, significantly outperforming pure and Ca-doped TiO2. The improved performance is attributed to bandgap reduction, defect-state formation, enhanced surface activity, and efficient charge transfer. These findings demonstrate that post-calcination nitrogen incorporation into Ca-doped TiO2 is an effective strategy for developing stable, visible-light-responsive photocatalysts for sustainable textile wastewater treatment.
Silver ion (Ag+) crosslinked CN/GO loaded carrageenan/alginate binary polysaccharide gel beads were first prepared as a heterogeneous photocatalyst. After reducing the crosslinked Ag+ to Ag0 under ultraviolet light, the Ag/CN/GO-GB catalyst was obtained and used for photodegradation of Crystal Violet (CV) under visible light. When the CN load content is 0.015 g, the Ag/CN/GO-GB1.5 composite has the highest degradation rate (99%) for CV in 60 min, which is 2 times that of CN. This high photodegradation rate is attributed to the excellent adsorption capacity of the polysaccharide to CV and the synergistic effect between Ag, CN and GO. In addition, the gel bead catalyst is easy to separate after use, which has important practical significance. This work opens up new ideas for ion-crosslinked polysaccharide gel beads and may inspire subsequent research.
Oil shale especially with low- to moderate maturity represents a strategically important resource due to its abundant reserves and wide global distribution. However, efficient exploration and enhanced recovery of product oil and gas remain challenging with current technologies. In this study, CuO nanosheet catalyst was synthesized and applied to oil shale pyrolysis. The catalyst promotes the cracking of long-chain hydrocarbons into shorter chains, significantly increasing the proportion of light fractions (gasoline and diesel) in product oil and improving overall oil quality. Simultaneously, shale gas production is notably enhanced, primarily in the form of low-molecular-weight methane and hydrogen. CuO nanosheet reduces the pyrolysis temperature and increases conversion efficiency of convertible organic matter into hydrocarbons, leading to improved hydrocarbon recovery rate. Density Functional Theory (DFT) calculations revealed spontaneous adsorption of kerogen molecules on the surface of CuO nanosheets, with reduced energy barriers for CC and CO bond cleavage. This study provides probable application prospects for the development of unconventional oil shale.
Catalytic hydrodeoxygenation of biomass-derived oxygenates to deoxygenated chemicals and fuels is a major research area, but selective production of aromatic compounds remains challenging, because complete deoxygenation favors formation of saturated alkanes and cycloalkanes. In this study, a highly dispersed ruthenium‑titanium oxide aerogel catalyst was synthesized via co-gelation of ruthenium and titanium precursors for the hydrodeoxygenation of lignin-derived guaiacol, which demonstrated good selectivity toward aromatic compounds, yielding 23% benzene and 47% phenol, with 48% oxygen atom removal. The catalyst's complex structure, comprising titanium oxide and ruthenium nanoclusters, was characterized using experimental methods and density functional theory calculations, which suggest that the synergy between ruthenium single atoms, nanoclusters, particles, and titanium oxide improves the selective conversion of guaiacol to benzene.
