Influence of pretreatment conditions on low-temperature CO oxidation over Pd supported UiO-66 catalysts

Shape-controlled hollow Cu2O@CuS nanocubes with enhanced photocatalytic activities towards degradation of tetracycline

In view of recent advances in photodegradation of antibiotics, low cost and stable photocatalyst remain rare. In this article, shape-controlled Cu2O@CuS nanocubes with the larger specific surface area were successfully prepared via a simple template-engaged strategy. Cu2O nanocubes were synthesized through a reduction method as original templates, the core-shelled Cu2O@CuS nanocubes were formed by sulphuration with Na2S as sulphur source, and the Cu2O core can be incompletely removed by Na2S2O3 to generate the Cu2O@CuS nanoboxes. Herein, hierarchical nanoboxes with two-layered Cu2O@CuS were used as photocatalyst materials for photocatalytic degradation of tetracycline (TC). The obtained nanocubes manifested high specific surface area (39.65 m2 g-1) and large pore volume (12.3 cm3 g-1). The degradation performance for TC was investigated in detail, including the effect of parameters such as photocatalyst, pH and catalyst dosage. The results indicated that degradation efficiencies were higher than 90% under visible light. Moreover, the degradation efficiency was 71% after six times.

Chlorine-Coordinated Pd Single Atom Enhanced the Chlorine Resistance for Volatile Organic Compound Degradation: Mechanism Study

The development of catalysts with high chlorine resistance for volatile organic compound (VOC) degradation is of great significance to achieve air purification. Herein, Pd@ZrO₂ catalysts with monodispersed Pd atoms coordinated with Cl were prepared using an in situ grown Zr-based metal-organic framework (MOF) as the sacrifice templates to enhance the chlorine resistance for VOC elimination. The residual Cl species from the Zr-MOF coordinated with Pd, forming Pd₁-Cl species during the pyrolysis. Meanwhile, abundant oxygen vacancies (V_O) were generated, which enhanced the adsorption and activation of gaseous oxygen molecules, accelerating the degradation of VOCs. In addition, the Pd@ZrO₂ catalysts exhibited satisfactory water resistance, long-term stability, and great resistance to CO and dichloromethane (DCM) for VOC elimination. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results elucidated that the generation of Pd₁-Cl species in Pd@ZrO₂ suppressed the absorption of DCM, releasing more active sites for toluene and its intermediate adsorption. Simultaneously, the monodispersed Pd atoms and V_O improved the reactivity of gaseous oxygen molecule adsorption and dissociation, boosting the deep decomposition of toluene and its intermediates. This work may provide a new strategy for rationally designing high-chlorine resistance catalysts for VOC elimination to improve the atmospheric environment.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

Stability of Pt-Adsorbed CO on Catalysts for Room Temperature-Oxidation of CO

A large signal of gas-phase CO overlapping with those of adsorbates is often present when investigating catalysts by operando diffuse reflectance FT-IR spectroscopy. Physically removing CO(g) from the IR cell may lead to a fast decay of adsorbate signals. Our work shows that carbonyls adsorbed on metallic Pt sites fully vanished in less than 10 min at 30 °C upon removing CO(g) when redox supports were used. In contrast, a broad band assigned to CO adsorbed on oxidized Pt sites was stable. It was concluded that physically removing CO(g) at room temperature during IR analyses will most likely lead to changes in the distribution of CO(ads) and a misrepresentation of the Pt site speciation, misguiding the development of efficient low-temperature CO oxidation catalysts. A tentative representation of the nature of the Pt phases present depending on the feed composition is also proposed.

Application of sulfate radicals-based advanced oxidation technology in degradation of trace organic contaminants (TrOCs): Recent advances and prospects

The large amount of trace organic contaminants (TrOCs) in wastewater has caused serious impacts on human health. In the past few years, Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal rates of recalcitrant TrOCs from water. Peroxymonosulfate (PMS) and persulfate (PS) are stable and non-toxic strong oxidizing oxidants and can act as excellent SO₄^•- precursors. Compared with hydroxyl radicals(·OH)-based methods, SR-AOPs have a series of advantages, such as long half-life and wide pH range, the oxidation capacity of SO₄^•- approaches or even exceeds that of ·OH under suitable conditions. In this review, we present the progress of activating PS/PMS to remove TrOCs by different methods. These methods include activation by transition metal, ultrasound, UV, etc. Possible activation mechanisms and influencing factors such as pH during the activation are discussed. Finally, future activation studies of PS/PMS are summarized and prospected. This review summarizes previous experiences and presents the current status of SR-AOPs application for TrOCs removal. Misconceptions in research are avoided and a research basis for the removal of TrOCs is provided.

Iron-based materials for simultaneous removal of heavy metal(loid)s and emerging organic contaminants from the aquatic environment: Recent advances and perspectives

The existence of heavy metals and emerging organic contaminants in wastewater produces serious toxic residues to the environment. Developing cheap and efficient materials to remove these persistent pollutants is crucial. Iron-based materials are cost-effective and environmentally friendly catalysts, and their applications in the environmental field deserve attention. This paper critically reviewed the removal mechanisms of heavy metals and emerging organic pollutants by different influencing factors. The removal of pollutants (heavy metals and emerging organic pollutants) in a multi-component system was analyzed in detail. The mechanisms of synergism, antagonism and non-interference were discussed. This paper had a certain reference value for the research of wastewater remediation technology which could simultaneously remove various pollutants by iron-based materials.

Degradation of norfloxacin by MOF-derived lamellar carbon nanocomposites based on microwave-driven Fenton reaction: Improved Fe(III)/Fe(II) cycle

In this paper, a new type of iron-based magnetic nanoparticle material embedding mesoporous carbon (Fe@C₇₀₀) was prepared by simple pyrolysis of a MIL-101-Fe precursor and employed in the microwave-catalyzed degradation of norfloxacin (NOR) with the presence of H₂O₂. Characterization results showed successful anchoring of Fe⁰ nanoparticles in the carbon matrix. Under optimal treatment conditions (Calcination temperature = 700 °C, H₂O₂ dosage = 40 mM, MW power = 500 W, NOR dosage = 50 mg L^-1 and initial pH = 4), the degradation efficiency of NOR reached 95.22%. The catalyst showed exceptional degradation properties over a relatively wide pH range. The mesoporous carbon in the catalyst promoted electron transfer, enhanced the Fe(III)/Fe(II) cycle, increased contact between Fe⁰ and Fe²⁺ with H₂O₂, and accelerated the production of ·OH. Furthermore, density functional theory (DFT) calculations were used to predict the fragile active sites in NOR and to analyze the degradation pathway of NOR in combination with intermediates. Fe@C₇₀₀ retained good activity after 5 cycles. Reduced toxicity of intermediates predicted by T.E.S.T. compared to NOR. This study presented a new avenue for the rational design of Fe⁰-carbon composites as microwave-assisted Fenton-like catalysts for potential applications in wastewater treatment.

Simply synthesized sodium alginate/zirconium hydrogel as adsorbent for phosphate adsorption from aqueous solution: Performance and mechanisms

The traditional zirconium hydrogel beads were synthesized by multi-step method, which was comparatively complex. In this study, a high phosphate removal efficient sodium alginate/zirconium (SA/Zr) hydrogel was synthesized by a simple method, with the phosphate adsorption performance and mechanism be explored. The results showed that the adsorption capacity of SA/Zr hydrogel to phosphate was greatly affected by pH. With the increase of initial pH (3-11), the adsorption capacity of SA/Zr for phosphate descended. The phosphate adsorption capacity of SA/Zr hydrogel exceeded 120 mg PO₄^3-/g at pH 2-7, while reaching the maximum adsorption capacity at pH 3 (256.79 mg PO₄^3-/g). The process of adsorption kinetics was well fitted by intraparticle diffusion model, indicating that there was chemical adsorption during the adsorption process. The Redlich-Peterson isotherm model can well accord with isotherm data. In addition, the material showed high selectivity to phosphate. Besides, combining X-ray photoelectron spectroscopy with Zeta potential results suggested that when the pH value was less than 4.19, SA/Zr hydrogel adsorbed phosphate by electrostatic attraction and hydrogen bonding while the adsorption was made mainly through ligand exchange when pH value was higher than 4.19.

Cobalt Phthalocyanine Supported on Mesoporous CeO2 as an Active Molecular Catalyst for CO Oxidation

Heterogenization of biomolecules by immobilizing on a metal oxide support could greatly enhance their catalytic activity and stability, but their interactions are generally weak. Herein, cobalt phthalocyanine (CoPc) molecules were firmly anchored on a Ce-based metal-organic framework (Ce-BTC) due to π-π stacking interaction between CoPc and aromatic frameworks of the BTC linker, which was followed by a calcination treatment to convert Ce-BTC to mesoporous CeO₂ and realize a molecular-level dispersion of CoPc on the surface of CeO₂. Various characterization results confirm the successful fabrication of molecular-based CoPc/CeO₂ catalysts which exhibited good CO oxidation performance. Importantly, we found that the mixing manner of Ce-BTC and CoPc remarkably affects the physicochemical properties which then determined the catalytic performance of the resultant CoPc/CeO₂ catalysts. In contrast, the direct physical mixing of CoPc and CeO₂ led to poor performance toward CO oxidation, manifesting that the Ce-BTC-mediated CoPc loading strategy is promising for the heterogenization of catalytic biomolecules.

Preparation of H3PO4 modified Sidr biochar for the enhanced removal of ciprofloxacin from water

In this study, biochar was prepared from Sidr plant leaves and used for the treatment of ciprofloxacin (CIP)-contaminated water. CIP is important class of emerging water pollutants from pharmaceutical industries. The biochar showed 65% adsorption efficiency and 43.48 mg/g adsorption capacity of CIP. Adsorption efficiency as well as adsorption capacity were improved to 91% and 62.50 mg/g, respectively, by phosphoric acid (H₃PO₄) modified biochar. Removal of CIP by the prepared biochar was due to different surface functional groups of CIP and biochar as revealed from the study of different characterization analyses. The presence of PO₄^3- group in modified biochar led to maximum binding of CIP. Also, the modified biochar showed higher reusability potential and less leaching of ions when compared to the raw biochar. Removal of CIP was affected by concentrations of CIP, the amount of biochar and different pH's; the maximum removal of CIP was achieved at pH 4. The Freundlich and pseudo-first-order models best fitted the removal of CIP by modified biochar. Advanced characterization techniques were applied to investigate surface and physiological characteristics of the biochar and modified biochar. The modification showed high impact on the performance and stability of biochar. The study showed significant impacts of modification on the potential of the biochar for treatment of CIP-contaminated water.

Enhanced removal of Cr(VI) from aqueous solution by stabilized nanoscale zero valent iron and copper bimetal intercalated montmorillonite

Batch experiments were conducted to study the Cr(VI) removal by nanoscale zero valent iron and copper intercalated montmorillonite (MMT-nFe⁰/Cu⁰) nanocomposite. MMT-nFe⁰/Cu⁰ was characterized using SEM, TEM, XRD, FTIR, N₂ adsorption-desorption isotherms and XPS. The results demonstrated that highly dispersed nanoscale Fe⁰/Cu⁰ (nFe⁰/Cu⁰) were successfully introduced into the montmorillonite (MMT) layers. In the reaction process, the combination of Cu⁰ and Fe⁰ acted as a galvanic cell, and electrocorrosion not only speeded up the reaction rate, but also increased reduction activity of nFe⁰. MMT-nFe⁰/Cu⁰ as an excellent carrier had good functions in dispersing nFe⁰ and Cu⁰ particles, pH buffering and could keep nFe⁰ and Cu⁰ particles from being released. Besides, no iron ions and very low concentrations of copper ions released in the reaction system, which greatly avoided the influence of secondary environmental pollution.

Ru-incorporated Co3O4 nanoparticles from self-sacrificial ZIF-67 template as efficient bifunctional electrocatalysts for rechargeable metal-air battery

Ru-incorporated Co₃O₄ nanoparticles have been synthesized from self-sacrificial ZIF-67 template and utilized as efficient electrocatalysts towards oxygen reduction and evolution reactions (ORR and OER). Amongst, Ru@Co₃O₄-1.0 exhibited the optimum electrocatalytic behavior with an ultra-low potential gap (0.84 V) between the OER potential (1.61 V at 10 mA cm^-2) and ORR half-wave potential (0.77 V). The zinc-air battery using Ru@Co₃O₄-1.0 as a cathode presented high specific capacity (788.1 mAh g^-1) and power density (101.2 mW cm^-2). Meanwhile, this battery possessed relatively lower voltage gap and higher cycling stability compared with the commercial Pt/C-based one. Ruthenium incorporation induced remarkable lattice expansion of Co₃O₄ and engineered more oxygen vacancies, promoting the lattice oxygen mobility from the subsurface/bulk phase onto surface. All these properties were recognized to be the crucial parameters for electrocatalytic activity improvement. This work provided a facile approach to design highly active metal oxide with broad potentiality for rechargeable metal-air batteries.

Effective Breaking of the Fluorocarbon Chain by the Interface Bi2O2X···PFOA Complex Strategy via Coordinated Se on Construction of the Internal Photogenerated Carrier Pathway

The destruction of perfluorooctanoic acid (PFOA) from outside was inhibited by the "barrel spiral" barrier, but the construction of the photocatalyst-PFOA complex provided a direct attack on photogenerated reactive species (RSs). Here, we investigated the bridging ability of bismuth oxychalcogenide (Bi₂O₂X) for constructing an effective photocarrier pathway to PFOA. The experimental results and DFT calculations showed that a more intense internal access of Bi₂O₂Se was built via the terminal carboxylate tail, and the weaker electrostatic interaction of Bi-Se bonds helped realize the smaller band gap and slower recombination of photocarriers, thereby inhibiting the invalid annihilation of holes with H₂O and facilitating the transformation of electrons to O₂^-•. The pseudo-first-order rate coefficient (k_obs) was 2 and 4 times higher than Bi₂O₂S and TiO₂, respectively, showing the outstanding photocatalytic activity of Bi₂O₂Se. A broad pH (4-8) adaptability of Bi₂O₂Se was observed for defluorination, especially in alkali condition. This new understanding may inspire the development of Se-coordinated catalysts.

Fabrication of MnCoOx composite oxides for catalytic CO oxidation via a solid-phase synthesis: The significant effect of manganese precursor

A series of Mn3Co16Ox composite oxides catalysts were fabricated via a solid-phase synthesis using different manganese precursors (namely as manganese acetate (A), nitrate (N), and sulfate (S)). It has been...

Rationally Tailoring Pore and Surface Properties of Metal-Organic Frameworks for Boosting Adsorption of Dy3

The adsorption and recovery of dysprosium ions (Dy³⁺) from industrial wastewater are necessary but still challenging. Herein, we constructed a series of defect-containing metal-organic frameworks (MOFs) [UiO-66-(COOH)₂] using sodium benzoate (BCNa) as a modulator. Upon the formation of defects, the porosity and surface charge properties of the MOFs were improved, leading to a higher utilization ratio of active groups and higher adsorption capacities for Dy³⁺. The synthesized UiO-66-(COOH)₂-B10 with an optimal addition of BCNa exhibited a superior adsorption capacity of 150.6 mg g^-1. Fast adsorption occurred at ∼5 min, and equilibrium was reached at ∼60 min. Higher pH and temperature were found to be beneficial for boosting Dy³⁺ adsorption, and selective adsorption over other metal ions was achieved in a multicomponent solution. Further, FTIR spectroscopy and XPS investigations indicate that free carboxyl contributes to the capture of Dy³⁺. Thus, this work provides a promising strategy to enhance the utilization ratio of active groups and further adsorption performance.

Microwave-assisted synthesis of manganese oxide catalysts for total toluene oxidation

Oxygen vacancy on the heterogeneous catalyst is of great importance to the catalysis of volatile organic compound (VOC) oxidation. Herein, microwave radiation with special energy-excitation is successfully utilized for the post-processing of a series of manganese oxides (MnO_x) to generate oxygen vacancies. It is found that the MnO_x catalyst with 60 min of microwave radiation demonstrates higher activity for toluene oxidation with a T_50% of 210 °C and a T_100% of 223 °C, which is attributed to the higher concentration of oxygen vacancies derived from the rich phase interface defects resulted from the microwave radiation. Furthermore, the Mn-MW-60 catalyst possesses excellent thermal stability and water vapor tolerance even under 20 vol% H₂O atmospheres within 60 h. In situ DRIFTS analysis verifies that both surface and lattice oxygen species simultaneously participate the oxidation process, and all reactions over different environments follows two different pathways. Meanwhile, it is proposed that those oxygen vacancies derived from microwave radiation could facilitate the rate-controlling step of opening the aromatic ring based on the electron back-donation, thereby leading to the increment of catalytic activity.

The high thermal stabilizing capability of noble metals (Pd and Au) supported by SBA-15 and the impact on CO oxidation

Precious metal nanoparticles (NPs) are attractive for use in the field of catalysis because of their precisely controlled sizes and shapes.

Selective oxidation of cyclopentene to glutaraldehyde by H2O2 over Nb-SBA-15

Cyclopentene was oxidized to glutaraldehyde over catalyst Nb2O5-SBA-15. The reaction was monitored with in situ ATR-FTIR.