In-situ DRIFT investigation of photocatalytic reduction and oxidation properties of SiO2@α-Fe2O3 core-shell decorated RGO nanocomposite

Mechanistic insights into the impact of bromide ion adsorption and surface bromination on Cu2O for enhanced selectivity and activity in electrochemical CO2 reduction

The enhanced selectivity for C2+ products in the electrochemical CO2 reduction reaction (ECO2RR) is critically dependent on the regulation of the elemental existence state on the surface of the electrocatalyst. In this study, Cu2O nanowires featuring multiple grain boundaries were successfully synthesized. Two distinct model catalysts were prepared: one through surface adsorption of Br- (denoted as Cu2O_Br) and the other via surface bromination (denoted as Cu2O@CuBr). These models were employed to systematically investigate the influence of the differences between Br- adsorption on the Cu2O surface and surface bromination on activity and product selectivity. The integration of in-situ characterization techniques with electrochemical measurements revealed that Br- adsorption induces a stable charge distribution on the catalyst surface, accompanied by a consistent potential drop within the double layer. This signifies stable and efficient processes of CO2 adsorption, electron transfer, and mass transfer at the electrode/electrolyte interface. Under these conditions, Cu2O_Br exhibits high stability. In contrast, catalyst surfaces modified via surface bromination are prone to Br- dissolution during electrolysis, leading to structural changes and significant surface reconstruction, which ultimately compromise the catalyst's selectivity. Notably, the Cu2O_Br catalyst achieved a maximum Faradaic efficiency (FE) of 98 % for CO production at -0.4 V vs. RHE and 42 % for C2H6 production at -0.6 V vs. RHE. Additionally, the Cu2O_Br catalyst reached an optimal FEC2+ of 60 % at -0.6 V, which is 1.5 times higher than that of the pure Cu2O catalyst under the same potential and 2.5 times higher than that of the Cu2O@CuBr catalyst at -0.9 V. This work provides new insights into enhancing the selectivity and activity of carbon dioxide electroreduction by modulating halide ion adsorption on the catalyst surface and surface halogenation.

Electrochemically grown porous platinum for electrocatalysis and optical applications

Localized electrochemically grown porous platinum layers on 2D and 3D microstructured materials enable a wide range of applications from electrocatalysis to optoelectronics. These layers exhibit a thickness gradient and surface corner overloading due to electric charge accumulation at the sharp corners. On one hand, these effects can be applied to create ultra-large surface area catalysts or electrocatalysts. On the other hand, they can be mitigated by guiding the electric field at the nanoscale. Here, we show that porous platinum grown on rough conductive silicon synergistically catalyses the electroreduction of CO2 in a humid gaseous atmosphere, overcoming the disadvantage of CO2´s low water solubility. In addition, using template-directed growth of porous platinum, we tuned the optical response of an infrared (IR) metamaterial fabricated by micropatterning on Si/NiCr/Ti substrates and constructed a broad absorber on potential IR-functional microcomponents.

Highly Selective CO2 Conversion to CH4 by a N-Doped HTiNbO5/NH2-UiO-66 Photocatalyst without a Sacrificial Electron Donor

Photocatalytic reduction of CO2 to value-added chemicals is a promising technology for reducing atmospheric CO2, but selectively producing a specific product still remains a great challenge. In this study, a Z-scheme heterojunction, N-doped HTiNbO5/NH2-UiO-66(Zr) (referred to as NH-NU), is developed to integrate the advantages of semiconductor photocatalysts and porous CO2 adsorbents for CO2-to-CH4 conversion. The NH-NU Z-scheme heterojunctions are fabricated via a simple one-pot solvothermal method, enabling the formation of a tight and uniform interface between the two phases, thereby facilitating the separation and transfer of the photoinduced charge carriers, as confirmed by TEM, EPR, electrochemical studies, and work functions. As a result, the as-prepared photocatalyst demonstrates a significant increase in selectivity for CH4 production through CO2 photoreduction, achieving a 10-fold enhancement compared to that of the pristine MOF, NH2-UiO-66. Moreover, there is no obvious decrease in the photocatalytic activity for CH4 production across four consecutive cycles. In situ FT-IR spectroscopy and DFT calculations reveal that charge-enriched N-doped NH-NU-3 composites stabilize various C1 intermediates in multistep elementary reactions, leading to superior selectivity in the CO2-to-CH4 conversion process. This work establishes that efficient and selective heterogeneous catalytic processes can be achieved through the stabilization of reaction intermediates by designing suitable Z-scheme heterojunctions.

Polyindole-Functionalized RGO-NiFe2O4-SiO2 Nanocomposite: A Dual-Functional Nanomaterial for Efficient Antimony Adsorption and Subsequent Application in Supercapacitor

Effective wastewater treatment remains a critical challenge, especially when dealing with hazardous pollutants like antimony (Sb(III)). This study addresses this issue by using innovative nanocomposites to remove Sb(III) ions from water, while simultaneously repurposing the spent adsorbents for energy storage applications. We developed reduced graphene oxide-NiFe2O3-SiO2-polyindole nanocomposites (RGO-NiFe2O3-SiO2-PIn NCs) via a hydrothermal synthesis method, achieving a high removal efficiency of 91.84% for Sb(III) ions at an initial concentration of 50 mg/L at pH 8. After adsorption, the exhausted adsorbent was repurposed for energy storage, effectively minimizing secondary pollution. The Sb(III)-loaded adsorbent (RGO-NiFe2O3-SiO2-PIn@SbOx) exhibited excellent performance as an energy storage material, with a specific capacitance (Cs) of 701.36 F/g at a current density of 2 A/g and a retention rate of 80.15% after 10,000 cycles. This dual-purpose approach not only advances wastewater treatment technologies but also contributes to sustainable and economical recycling practices, particularly in the field of energy storage.

Modeling sustainable photocatalytic degradation of acidic dyes using Jordanian nano-Kaolin-TiO2 and solar energy: Synergetic mechanistic insights

The abstract highlights the global issue of environmental contamination caused by organic compounds and the exploration of various methods for its resolution. One such approach involves the utilization of titanium dioxide (TiO2) as a photocatalyst in conjunction with natural adsorption materials like kaolin. The study employed a modeling-based approach to investigate the sustainable photocatalytic degradation of acidic dyes using a Jordanian nano-kaolin-TiO2 composite material and solar energy. Mechanistic insights were gained through the identification of the dominant reactive oxygen species (ROS) involved in the degradation process, as well as the synergetic effect between adsorption and photocatalysis. The Jordanian nano-kaolin-TiO2 composite was synthesized using the sol-gel method and characterized. The nanocomposite photocatalyst exhibited particle sizes ranging from 27 to 41 nm, with the TiO2 nanoparticles well-dispersed within the kaolin matrix. The efficacy of this nanocomposite in removing Congo-red dye was investigated under various conditions, including pH, initial dye concentration, and photocatalyst amount. The optimal conditions for dye removal were found to be at pH 5, with an initial dye concentration of 20 ppm, and using 0.1 g of photocatalyst, resulting in a 95 % removal efficiency. The mechanistic insights gained from this study indicate that the hydroxyl radicals (•OH) generated during the photocatalytic process play a dominant role in the degradation of the acidic dye. Furthermore, the synergetic effect between the adsorption of the dye molecules onto the photocatalyst surface and the subsequent photocatalytic degradation by the ROS was found to enhance the overall removal efficiency. These findings contribute to the fundamental understanding of the photodegradation mechanisms and guide the development of more efficient photocatalytic systems for the treatment of acidic dye-containing wastewater. The use of solar power during the purification procedure also leads to cost reduction and strengthens sustainability efforts.

Thermocatalytic oxidation of a binary mixture of formaldehyde and toluene at ambient levels by a titanium dioxide supported platinum catalyst

The thermocatalytic oxidative potential of various supported noble metal catalysts (SNMCs) is well-known for hazardous volatile organic compounds (VOCs), e.g., formaldehyde (FA) and toluene. However, little is known about SNMC performance against ambient VOC pollution with low concentration (subppm levels) relative to industrial effuluents with high concentrations (several hundred ppm). Here, the thermocatalytic oxidation performance of a titanium dioxide (TiO2)-supported platinum catalyst (Pt/TiO2) has been evaluated for a low-concentration binary mixture of FA and toluene at low temperatures and in the dark. A sample of TiO2 containing 1 wt% Pt with thermal reduction pre-treatment under hydrogen achieved 100 % conversion of FA (500 ppb) and toluene (100 ppb) at 130 °C and a gas hourly velocity of 59,701 h-1. Its catalytic activity was lowered by either a decrease in catalyst mass or an increase in VOC concentration, relative humidity, or flow rate. In situ diffuse reflectance infrared Fourier transform spectroscopy, density functional theory simulations, and molecular oxygen (O2) temperature-programmed desorption experiments were used to identify possible VOC oxidation pathways, reaction mechanisms, and associated surface phenomena. The present work is expected to offer insights into the utility of metal oxide-supported Pt catalysts for the low-temperature oxidative removal of gaseous VOCs in the dark, primarily for indoor air quality management.

Boosting photocatalytic CO2 conversion using strongly bonded Cu/reduced Nb2O5 nanosheets

Green energy production is becoming increasingly important in mitigating the effects of climate change, and the photocatalytic approach could be a potential solution. However, the main barriers to its commercialization are ineffective catalysis due to recombination, poor optical absorption, and sluggish carrier migration. Here, we fabricated a two-dimensional (2D) reduced niobium oxide photocatalyst synthesized by an in situ thermal method followed by copper incorporation. Compared to its counterparts, pure Nb2O5 (0.092 mmol g-1 CO) and r-Nb2O5 (0.216 mmol g-1 CO), the strongly bonded Cu/r-Nb2O5 (0.908 mmol g-1) sample produced an exceptional amount of CO. The separation of charge carriers and efficient use of light resulted in a remarkable photocatalytic performance. The acceptor levels were created by the Cu nanophase, and the carrier trapping states were created by the oxygen vacancies. This mechanism was supported by ESR and DRIFT analyses, which showed that enough free radicals were produced. This study opens up new possibilities for developing efficient photocatalysts that will generate green fuel.

Construction of SnO2/CuO/rGO nanocomposites for photocatalytic degradation of organic pollutants and antibacterial applications

Water contamination by reactive dyes is a serious concern for human health and the environment. In this study, we prepared high efficient SnO₂/CuO/rGO nanocomposites for reactive dye degradation. For structural analysis of SnO₂/CuO/rGO nanocomposites, XRD, UV-Vis DRS, SEM, TEM-EDAX, and XPS analysis were used to characterize the physicochemical properties of the material. The characterization results confirmed great crystallinity, purity, and optical characteristics features. For both Rhodamine B (RhB) and Reactive Red 120 (RR120) degradation processes, SnO₂/CuO/rGO nanocomposites were tested for their photocatalytic degradation performance. The SnO₂/CuO/rGO nanocomposites have expressed the degradation rate exposed to 99.6% of both RhB and RR120 dyes. The main reason behind the photocatalytic degradation was due to the formation of OH radical's generation by the composite materials. Moreover, the antibacterial properties of synthesized SnO₂/CuO/rGO nanocomposites were studied against E. coli, S. aureus, B. subtilis and P. aeroginosa and exhibited good antibacterial activity against the tested bacterial strains. Thus, the synthesized SnO₂/CuO/rGO nanocomposites are a promising photocatalyst and antibacterial agent. Furthermore, mechanisms behind the antibacterial effects will be ruled out in near future.

Understanding the intermediates and carbon dioxide adsorption of potassium chloride-incorporated graphitic carbon nitride with tailoring melamine and urea as precursors

In this study, we demonstrated the synthesis of potassium chloride (KCl)-incorporated graphitic carbon nitride, (g-C₃N₄, CN) with varying amounts of N-vacancies and pyridinic-N as well as enhanced Lewis basicity, via a single-step thermal polymerization by tailoring the precursors of melamine and urea for carbon oxide (CO₂) capture. Melamine, as a precursor, undergoes a phase transformation into melam and triazine-rich g-C₃N₄, whereas the addition of urea polymerizes the mixture to form melem and heptazine-rich g-C₃N₄ (CN11). Owing to the abundance of pyridinic-N and the high surface area, CN11 adsorbed higher amounts of CO₂ (44.52 μmol m^-2 at 25 °C and 1 bar of CO₂) than those reported for other template-free carbon materials. Spectroscopic analysis revealed that the enhanced CO₂ adsorption is due to the presence of pyridinic-N and Lewis basic sites on the surface. The intermediates of CO₂adsorption, including carbonate and bicarbonate species, attached to the CN samples were identified using in-situ Fourier-transform infrared spectroscopy (FTIR). This work provides insights into the mechanism of CO₂ adsorption by comparing the structural features of the synthesized KCl-incorporated g-C₃N₄ samples_. CN11, with an excellent CO₂ uptake capacity, is viewed as a promising candidate for CO₂ capture and storage.

Sensitive colorimetric glucose sensor by iron-based nanozymes with controllable Fe valence

The proportion of Fe2+ and Fe3+ in Fe-based nanozymes is a key point in determining their catalytic activity. However, it is hard to adjust the Fe2+/Fe3+ ratio in nanozyme systems to achieve the best catalytic performance. In this work, we successfully regulate Fe2+/Fe3+ ratios in a wide range of 0.81-1.45 based on a novel porous platform of Fe doped silica hollow spheres. The homogeneous distribution and stable fixation of Fe components in Fe doped silica hollow spheres facilitate the valence regulation of Fe in the reduction heating in H2/Ar. When the Fe doped spheres (FeOx@SHSs) were used as nanozymes, different Fe2+/Fe3+ ratios have shown to influence the peroxidase-like catalytic activity greatly. The highest activity at the ratio of 1.41 should be due to the combined effects of the accelerated reaction rate by Fe2+ and the enhanced catalytic cycle efficiency by Fe3+. The FeOx@SHSs-based nanozyme is further applied to construct a facile colorimetric biosensing system, which exhibited extremely sensitive determination of glucose. This work presents an effective platform for controlling Fe valences and optimizing the peroxidase-like activity for catalytic processes or sensing systems.

Bioinspired Assembly of Double Honeycomb-Like Hierarchical Capsule Confined Encapsulation with Functional Micro/Nanocrystals

Inspired by "micro/nanoreactor" effect of cellular organelle on specific biochemical reactions, a double honeycomb-like hierarchical capsule confined encapsulation with functional micro/nanocrystals is designed. The bioinspired hierarchical capsules derived from polymeric composite microspheres are successfully fabricated through a combination of selective chemical etching and pyrolysis. In situ introduction of functional guests (including organometallic molecules, tetraethoxysilane, or metal-organic frameworks (MOFs)) into internal cellular structure of microspheres is first put forward by phase inversion method. The development of selective etching creates honeycomb-like structure on the outside surface of capsule and allows sulfur to homogeneously distribute into matrix. With the novel approach, the hierarchical channels (micro-meso-macropore) of composite capsule enhance transportation of reactants and dispersion of active sites, and thus exhibit superior photocatalytic oxidation and electromagnetic absorbing. The promising strategy will be applied more generally to encapsulate different species into hierarchical capsule with tailored properties and functionalities.

Plasma-Catalysis for Volatile Organic Compounds Decomposition: Complexity of the Reaction Pathways during Acetaldehyde Removal

Acetaldehyde removal was carried out using non-thermal plasma (NTP) at 150 J·L−1, and plasma-driven catalysis (PDC) using Ag/TiO2/SiO2, at three different input energies—70, 350 and 1150 J·L−1. For the experimental configuration used, the PDC process showed better results in acetaldehyde (CH3CHO) degradation. At the exit of the reactor, for both processes and for all the used energies, the same intermediates in CH3CHO decomposition were identified, except for acetone which was only produced in the PDC process. In order to contribute to a better understanding of the synergistic effect between the plasma and the catalyst, acetaldehyde/catalyst surface interactions were studied by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). These measurements showed that different species such as acetate, formate, methoxy, ethoxy and formaldehyde are present on the surface, once it has been in contact with the plasma. A reaction pathway for CH3CHO degradation is proposed taking into account all the identified compounds in both the gas phase and the catalyst surface. It is very likely that in CH3CHO degradation the presence of methanol, one of the intermediates, combined with oxygen activation by silver atoms on the surface, are key elements in the performance of the PDC process.