Photocatalytic carbon dioxide reduction to methanol catalyzed by ZnO, Pt, Au, and Cu nanoparticles decorated zeolitic imidazolate framework-8

Emerging ZnO Semiconductors for Photocatalytic CO2 Reduction to Methanol

Carbon recycling is poised to emerge as a prominent trend for mitigating severe climate change and meeting the rising demand for energy. Converting carbon dioxide (CO2) into green energy and valuable feedstocks through photocatalytic CO2 reduction (PCCR) offers a promising solution to global warming and energy needs. Among all semiconductors, zinc oxide (ZnO) has garnered considerable interest due to its ecofriendly nature, biocompatibility, abundance, exceptional semiconducting and optical properties, cost-effectiveness, easy synthesis, and durability. This review thoroughly discusses recent advances in mechanistic insights, fundamental principles, experimental parameters, and modulation of ZnO catalysts for direct PCCR to C1 products (methanol). Various ZnO modification techniques are explored, including atomic size regulation, synthesis strategies, morphology manipulation, doping with cocatalysts, defect engineering, incorporation of plasmonic metals, and single atom modulation to boost its photocatalytic performance. Additionally, the review highlights the importance of photoreactor design, reactor types, geometries, operating modes, and phases. Future research endeavors should prioritize the development of cost-effective catalyst immobilization methods for solid-liquid separation and catalyst recycling, while emphasizing the use of abundant and non-toxic materials to ensure environmental sustainability and economic viability. Finally, the review outlines key challenges and proposes novel directions for further enhancing ZnO-based photocatalytic CO2 conversion processes.

Fabrication of Gold and Silver Nanoparticles Supported on Zinc Imidazolate Metal-Organic Frameworks as Active Catalysts for Hydrogen Release from Ammonia Borane

Well-dispersed Au and Ag nanoparticles (NPs) have been immobilized on a zinc imidazolate metal-organic framework, Zn(mim), using the "one-pot" method and tested as catalysts in ammonia borane hydrolysis. The AuNPs@Zn(mim) and AgNPs@Zn(mim) materials were characterized by FTIR, XRD, ICP-OES, TGA, BET, SEM, and TEM. The AgNPs@Zn(mim) catalyst showed a high yield (98.5%) and high hydrogen generation rate (3352.71 mL min-1 gAg -1) in NH3BH3 dehydrogenation. The determined activation energies (19.6 kJ mol-1 for AuNPs@Zn(mim) and 38.13 kJ mol-1 for AgNPs@Zn(mim)) are lower than those for most reported catalysts containing Au/Ag-MOF used in the hydrolysis of NH3BH3. Moreover, the catalysts tested here revealed good stability and reusability, preserving 71.42% (AuNPs@Zn(mim)) and 88.23% (AgNPs@Zn(mim)) of their initial catalytic activities after five consecutive cycles. In the case of AgNPs@Zn(mim), the combination of the simple and green synthesis method, low active metal content, relatively low cost, and moderate dehydrogenation conditions makes the material an excellent candidate to produce hydrogen from ammonia borane.

Unveiling the remarkable simultaneous adsorption-photocatalytic potential of Ag nanoparticles-anchored phosphotungestic acid loaded ZIF-8 for Congo red removal

This research paper presents a direct approach to synthesize AgNPs deposited on polyoxometalate/ZIF-8 on-site (referred to as AgNPS@PW@ZIF-8) to develop a highly efficient photocatalyst in the water treatment. Phosphotungestic acid (PW) serves a multi-purpose in this context: it acts as a bridge layer between AgNPs and Zeolitic Imidazolate Framework-8 (ZIF-8), a local reducing agent, and a catalyst for electron transfer during the photocatalysis process. A comprehensive characterization of the resulting nanostructure was performed utilizing an array of techniques, such as XRD, FTIR, EDX, TEM, BET, Raman, and TGA. The nanostructure that was created exhibited effective removal of Congo red at different pH levels via a combination of simultaneous adsorption and photocatalysis. After 60 min at pH 7, the dye molecules were completely eliminated in the presence of 0.5 g/L AgNPS@PW@ZIF-8 at room temperature. The charge transfer can be facilitated by the PW bridge layer connecting AgNPs and ZIF-8, owing to the photoactive characteristics and strong electron transfer capabilities of PW molecules. Strong electron transferability of PW between Ag nanoparticles and ZIF-8 facilitates charge transfer and significantly improves the photocatalytic performance of ZIF-8. Moreover, the nanostructure demonstrated great structural stability and recyclability, sustaining a high efficiency of removal throughout five consecutive cycles through the implementation of a simple procedure. Widespread applications of the developed nanostructure in aquatic environments for adsorption and photocatalytic reactions are possible.

Bimetal doped Cu-Fe-ZIF-8/g-C3N4 nanocomposites for the adsorption of tetracycline hydrochloride from water

Bimetal doped Cu-Fe-zeolitic imidazole framework-8 (ZIF-8)/graphitic carbon nitride (GCN) (Cu-Fe-ZIF-8/GCN) nanocomposites were prepared via one-pot and ion-exchange methods. The main influencing factors, such as adsorbent concentration, TC concentration, initial pH, and coexisting ions, were evaluated in detail. Due to the suitable pore structures and the presence of multiple interactions on the surface, the nanocomposite showed a high adsorption capacity up to 932 mg g-1 for tetracycline hydrochloride (TC), outperforming ZIF-8 by 4.8 times. The adsorption kinetics and adsorption isotherm were depicted in good detail using pseudo-second-order kinetic and Langmuir models, respectively. Thermodynamic calculation revealed that the adsorption of the nanocomposite under experimental conditions was a spontaneous heat absorption process, and was primarily driven by chemisorption. After four cycles of use, the nanocomposite retained 87.2% of its initial adsorption capacity, confirming its high reusability and broad application prospects in removing tetracycline-type pollutants from wastewater.

Unravelling Dynamics Involving Multiple Charge Carriers in Semiconductor Nanocrystals

The use of colloidal nanocrystals as part of artificial photosynthetic systems has recently gained significant attention, owing to their strong light absorption and highly reproducible, tunable electronic and optical properties. The complete photocatalytic conversion of water to its components is yet to be achieved in a practically suitable and commercially viable manner. To complete this challenging task, we are required to fully understand the mechanistic aspects of the underlying light-driven processes involving not just single charge carriers but also multiple charge carriers in detail. This review focuses on recent progress in understanding charge carrier dynamics in semiconductor nanocrystals and the influence of various parameters such as dimension, composition, and cocatalysts. Transient absorption spectroscopic studies involving single and multiple charge carriers, and the challenges associated with the need for accumulation of multiple charge carriers to drive the targeted chemical reactions, are discussed.

Assembling CeO2 nanoparticles on ZIF-8 via the hydrothermal method to promote the CO2 photoreduction performance

Photocatalytic reduction of CO₂ to valuable carbon fuel is a prospective technique to decrease CO₂ emissions and simultaneously generate efficient chemical energy. In this paper, a novel high-efficiency photocatalyst ZIF-8@CeO₂ heterogeneous composite (ZIF = zeolitic imidazolate framework) was prepared by the hydrothermal method, where CeO₂ nanospheres were uniformly grown on the surface of ZIF-8. Compared to pristine ZIF-8 or CeO₂ nanoparticles (NPs), the ZIF-8@CeO₂ composite shows significantly better efficiency in the reduction of CO₂ into CO and CH₄ under light irradiation, that is the CO evolution rate can reach 465.01 μmol g^-1 h^-1 and the CH₄ evolution rate can reach 181.27 μmol g^-1 h^-1. Analyses indicated that the addition of CeO₂ in the composites will expand the photoresponse region; the formation of the ZIF-8/CeO₂ heterojunction significantly promoted the separation of photogenerated electron-hole pairs within the composite. This work provided an effective method to further improve the catalytic activity of ZIF-based materials, which paved a new way for eco-friendly conversion of carbon dioxide into clean fuels and they could also have huge potential for application in energy and environmental science.

A Strategy for the Determination of Alkaline Phosphatase Based on the Self-Triggered Degradation of Metal-Organic Frameworks by Phosphate

Alkaline phosphatase (ALP) is widely present in the human body and is an important biomarker. Numerous ALP detection studies have been carried out, and ascorbic acid (AA) is often used as the reducing component in the sensors to monitor ALP levels since it can be produced from ascorbic acid 2-phosphate (AA2P) hydrolysis in the presence of ALP. However, it is well-known that AA is a strong reducing agent and can be easily oxidized. The disproportion between oxidized AA and reduced AA reactions results in the generation of AA free radicals with single electrons that may lead to inaccurate results in assays. To solve this problem, we synthesized a core-shell metal-organic framework sensor (PATP-Au@ZIF-8 NP) and used it as a sensitive and accurate ALP detection sensor with self-triggered control of phosphate ions (Pi) to avoid the potential inaccuracy of the method that uses AA as the reducing component. By establishing a physical shell on the surface of the gold nanoparticles (Au NPs), the sensor not only can eliminate the random assembly of metal nanoparticles caused by plasma exposure but also can generate self-triggering of Pi caused by ALP. Pi can decompose ZIF-8 through coordination with Zn²⁺ and thus can destroy the ZIF-8 shell structure of the prepared PAZ NPs. Au NPs are released and then become aggregated, in turn causing the SERS "hot spot" area to increase. The enhancement of the SERS signals was found to be directly associated with the level of Pi released from ALP-triggered hydrolysis. The response of the strategy was linear at ALP concentrations ranging from 0.1 to 150 mU/mL (r = 0.996) with a detection limit of 0.03 mU/mL. Lastly, the developed strategy was employed in the evaluation of ALP inhibitors, and the possibility to implement the developed SERS strategy for rapid and selective analysis of ALP in human serum was demonstrated.

Non-Noble Plasmonic Metal-Based Photocatalysts

Solar-to-chemical energy conversion via heterogeneous photocatalysis is one of the sustainable approaches to tackle the growing environmental and energy challenges. Among various promising photocatalytic materials, plasmonic-driven photocatalysts feature prominent solar-driven surface plasmon resonance (SPR). Non-noble plasmonic metals (NNPMs)-based photocatalysts have been identified as a unique alternative to noble metal-based ones due to their advantages like earth-abundance, cost-effectiveness, and large-scale application capability. This review comprehensively summarizes the most recent advances in the synthesis, characterization, and properties of NNPMs-based photocatalysts. After introducing the fundamental principles of SPR, the attributes and functionalities of NNPMs in governing surface/interfacial photocatalytic processes are presented. Next, the utilization of NNPMs-based photocatalytic materials for the removal of pollutants, water splitting, CO₂ reduction, and organic transformations is discussed. The review concludes with current challenges and perspectives in advancing the NNPMs-based photocatalysts, which are timely and important to plasmon-based photocatalysis, a truly interdisciplinary field across materials science, chemistry, and physics.

Metal Oxides as Catalyst/Supporter for CO2 Capture and Conversion, Review

Various carbon dioxide (CO2) capture materials and processes have been developed in recent years. The absorption-based capturing process is the most significant among other processes, which is widely recognized because of its effectiveness. CO2 can be used as a feedstock for the production of valuable chemicals, which will assist in alleviating the issues caused by excessive CO2 levels in the atmosphere. However, the interaction of carbon dioxide with other substances is laborious because carbon dioxide is dynamically relatively stable. Therefore, there is a need to develop types of catalysts that can break the bond in CO2 and thus be used as feedstock to produce materials of economic value. Metal oxide-based processes that convert carbon dioxide into other compounds have recently attracted attention. Metal oxides play a pivotal role in CO2 hydrogenation, as they provide additional advantages, such as selectivity and energy efficiency. This review provides an overview of the types of metal oxides and their use for carbon dioxide adsorption and conversion applications, allowing researchers to take advantage of this information in order to develop new catalysts or methods for preparing catalysts to obtain materials of economic value.

Recent Advances of Photocatalytic Hydrogenation of CO2 to Methanol

Constantly increasing hydrocarbon fuel combustion along with high levels of carbon dioxide emissions has given rise to a global energy crisis and environmental alterations. Photocatalysis is an effective technique for addressing this energy and environmental crisis. Clean and renewable solar energy is a very favourable path for photocatalytic CO2 reduction to value-added products to tackle problems of energy and the environment. The synthesis of various products such as CH4, CH3OH, CO, EtOH, etc., has been expanded through the photocatalytic reduction of CO2. Among these products, methanol is one of the most important and highly versatile chemicals widely used in industry and in day-to-day life. This review emphasizes the recent progress of photocatalytic CO2 hydrogenation to CH3OH. In particular, Metal organic frameworks (MOFs), mixed-metal oxide, carbon, TiO2 and plasmonic-based nanomaterials are discussed for the photocatalytic reduction of CO2 to methanol. Finally, a summary and perspectives on this emerging field are provided.

Photo-assisted effective and selective reduction of CO2 to methanol on a Cu–ZnO–ZrO2 catalyst

Highly selective catalysis of CO2 hydrogenation to methanol with photo-assistance on Cu–ZnO–ZrO2, a photothermal synergistic catalyst.

Bi-Functional Paraffin@Polyaniline/TiO2/PCN-222(Fe) Microcapsules for Solar Thermal Energy Storage and CO2 Photoreduction

A novel type of bi-functional microencapsulated phase change material (MEPCM) microcapsules with thermal energy storage (TES) and carbon dioxide (CO₂) photoreduction was designed and fabricated. The polyaniline (PANI)/titanium dioxide (TiO₂)/PCN-222(Fe) hybrid shell encloses phase change material (PCM) paraffin by the facile and environment-friendly Pickering emulsion polymerization, in which TiO₂ and PCN-222(Fe) nanoparticles (NPs) were used as Pickering stabilizer. Furthermore, a ternary heterojunction of PANI/(TiO₂)/PCN-222(Fe) was constructed due to the tight contact of the three components on the hybrid shell. The results indicate that the maximum enthalpy of MEPCMs is 174.7 J·g^-1 with encapsulation efficiency of 77.2%, and the thermal properties, chemical composition, and morphological structure were well maintained after 500 high-low temperature cycles test. Besides, the MEPCM was employed to reduce CO₂ into carbon monoxide (CO) and methane (CH₄) under natural light irradiation. The CO evolution rate reached up to 45.16 μmol g^-1 h^-1 because of the suitable band gap and efficient charge migration efficiency, which is 5.4, 11, and 62 times higher than pure PCN-222(Fe), PANI, and TiO₂, respectively. Moreover, the CO evolution rate decayed inapparently after five CO₂ photoreduction cycles. The as-prepared bi-functional MEPCM as the temperature regulating building materials and air purification medium will stimulate a potential application.

Preparation and Application of Nb2O5 Nanofibers in CO2 Photoconversion

Increasing global warming due to NOx, CO2, and CH4, is significantly harming ecosystems and life worldwide. One promising methodology is converting pollutants into valuable chemicals via photocatalytic processes (by reusable photocatalysts). In this context, the present work aimed to produce a Nb2O5 photocatalyst nanofiber system by electrospinning to convert CO2. Based on the collected data, the calcination at 600 ∘C for 2 h resulted in the best condition to obtain nanofibers with homogeneous surfaces and an average diameter of 84 nm. As a result, the Nb2O5 nanofibers converted CO2 mostly into CO and CH4, reaching values around 8.5 μmol g−1 and 0.55 μmol g−1, respectively.

Bismuth Oxyhalides for NOx Degradation under Visible Light: The Role of the Chloride Precursor

Photocatalysis is a green technology for tackling water and air contamination. A valid alternative to the most exploited photocatalytic material, TiO2, is bismuth oxyhalides, which feature a wider bandgap energy range and use visible radiation to attain photoexcitation. Moreover, their layered structure favors the separation of photogenerated electron–hole pairs, with an enhancement in photocatalytic activity. Controlled doping of bismuth oxyhalides with metallic bismuth nanoparticles allows for further boosting of the performance of the material. In the present work, we synthesized Y%Bi-doped BiO(Cl0.875Br0.125) (Y = 0.85, 1, 2, 10) photocatalysts, using cetyltrimethylammonium bromide as the bromide source and varying the chloride source to assess the impact that both length and branching of the hydrocarbon chain might have on the framing and layering of the material. A change in the amount of the reducing agent NaBH4 allowed tuning of the percentage of metallic bismuth. After a thorough characterization (XRPD, SEM, TEM, UV-DRS, XPS), the photocatalytic activity of the catalysts was tested in the degradation of NOx under visible light, reaching a remarkable 53% conversion after 3 h of illumination for the material prepared using cetylpyridinium chloride.