Reactive Intermediate Species Research Articles

Integrated CO2 capture and dynamic catalysis for CO2 recycling in a microbrewery

In this study, we used fermentation off-gases from a brewery for integrated CO2 capture and utilisation in order to produce CH4 with a dual-function material (DFM) containing NiRu as catalyst and dispersed CaO as adsorbent. CH4 was produced from captured CO2 via 2 pathways (fast and slow), proceeding through formyl intermediates according to the operando DRIFTS-MS results. The NiRuCa DFM showed a stable CH4 capacity over 8 cycles (105 μmol/gDFM) with fermentation off-gases being used as a CO2 capture feed. H2O and O2, which were present in small amounts in the emissions feed, resulted in the passivation of Ni in the form of a NiO layer and hence, the DFM did not undergo excessive oxidation and deactivation. This work constitutes a first in terms of validating the use of DFMs with real industrial emissions, and it directly correlates the DFM activity performance with its reaction mechanism and intermediate species.

Noble Metal‐Free High Entropy Perovskite Oxide with High Cationic Dispersion Enhanced Oxygen Redox Reactivity

AbstractHigh entropy perovskite oxide (HEPO) materials have received significant interest as efficient electrocatalysts owing to their chemical and structural stability, effective interaction of multiple metal active sites with the reaction intermediate species resulting in enhanced catalytic activity. The effect of high‐entropy strategy could achieve the regulation of the structural durability by tailoring the composition. Herein, we design a novel transition metal and rare‐earth metal based high entropy perovskite oxide (Co0.11Mn0.11Ni0.11Fe0.14La0.13Nd0.13Gd0.13Pr0.13)O3, showing superior catalytic activity in the oxygen reduction reaction (ORR) and also promising electrocatalyst in oxygen evolution reaction (OER). High degree of cationic dispersion in the lattice and multiple electrocatalytic active sites enhance the oxygen ion migration at the surface and facilitate electron transfer, manifesting good ORR performance. Notably, the as‐prepared high entropy material exhibits onset and half‐wave potential of 1.02 V and 0.89 V versus RHE, respectively, exceeding the performance of the benchmarked Pt/C catalyst in the ORR process with reasonable redox kinetics. Moreover, the material also presents faster kinetics with reasonably low overpotential and excellent electrochemical stability in the OER process as well. This study shows the viability of designing non‐precious high entropy materials as highly efficient oxide electrocatalyst by utilizing its broad compositional space.

Hydroxylamine-induced activation of permanganate for enhanced oxidation of sulfamethoxazole: Mechanism and products

Recently, many reagents have been introduced to accelerate the formation of highly reactive intermediate Mn species from permanganate (KMnO4), thereby improving the oxidation activity of KMnO4 towards pollutants. However, most studies have mainly focused on sulfur-containing reducing agents (e.g., bisulfite and sodium sulfite), with little attention paid to nitrogen-containing reducing agents. This study found that hydroxylamine (HA) and hydroxylamine derivatives (HAs) can facilitate KMnO4 in pollutant removal. Taking sulfamethoxazole (SMX) as a target contaminant, the effect of pH, SMX concentration, KMnO4 and HA dosages, and the molar ratio of HA and KMnO4 on the degradation of SMX in the KMnO4/HA process was systematically investigated. Quenching experiments and probe analysis revealed MnO2-catalyzed KMnO4 oxidation, Mn(III) and reactive nitrogen species as the primary active species responsible for SMX oxidation in the KMnO4/HA system. Proposed transformation pathways of SMX in the KMnO4/HA system mainly involve hydroxylation and cleavage reactions. The KMnO4/HA system was more conducive to selective oxidation of SMX, 2,4-dichlorophenol, and several other pollutants, but reluctant to bisphenol S (BPS). Overall, this study proposed an effective system for eliminating pollutants, while providing mechanistic insight into HA-driven KMnO4 activation for environmental remediation.

Pyrene‐Alkyne‐Based Conjugated Porous Polymers with Skeleton Distortion‐Mediated ⋅O2− and 1O2 Generation for High‐Selectivity Organic Photosynthesis

AbstractReactive oxygen species (ROS) play a crucial role in determining photocatalytic reaction pathways, intermediate species, and product selectivity. However, research on ROS regulation in polymer photocatalysts is still in its early stages. Herein, we successfully achieved series of modulations to the skeleton of Pyrene‐alkyne‐based (Tetraethynylpyrene (TEPY)) conjugated porous polymers (CPPs) by altering the linkers (1,4‐dibromobenzene (BE), 4,4′‐dibromobiphenyl (IP), and 3,3′‐dibromobiphenyl (BP)). Experiments combined with theoretical calculations indicate that BE‐TEPY exhibits a planar structure with minimal exciton binding energy, which favors exciton dissociation followed by charge transfer with adsorbed O2 to produce ⋅O2−. Thus BE‐TEPY shows optimal photocatalytic activity for phenylboronic acid oxidation and [3+2] cycloaddition. Conversely, the skeleton of BP‐TEPY is significantly distorted. Its planar conjugation decreases, intersystem crossing (ISC) efficiency increases, which makes it more prone for resonance energy transfer to generate 1O2. Therefore, BP‐TEPY displays best photocatalytic activity in [4+2] cycloaddition and thioanisole oxidation. Both above reactant conversion and its product selectivity exceed 99 %. This work systematically reveals the intrinsic structure–activity relationship among the skeleton structure of CPPs, excitonic behavior, and selective generation of ROS, providing new insights for the rational design of highly efficient and selective CPPs photocatalysts.

Pyrene-Alkyne-Based Conjugated Porous Polymers with Skeleton Distortion-Mediated ⋅O2 - and 1O2 Generation for High-Selectivity Organic Photosynthesis.

Reactive oxygen species (ROS) play a crucial role in determining photocatalytic reaction pathways, intermediate species, and product selectivity. However, research on ROS regulation in polymer photocatalysts is still in its early stages. Herein, we successfully achieved series of modulations to the skeleton of Pyrene-alkyne-based (Tetraethynylpyrene (TEPY)) conjugated porous polymers (CPPs) by altering the linkers (1,4-dibromobenzene (BE), 4,4'-dibromobiphenyl (IP), and 3,3'-dibromobiphenyl (BP)). Experiments combined with theoretical calculations indicate that BE-TEPY exhibits a planar structure with minimal exciton binding energy, which favors exciton dissociation followed by charge transfer with adsorbed O2 to produce ⋅O2 -. Thus BE-TEPY shows optimal photocatalytic activity for phenylboronic acid oxidation and [3+2] cycloaddition. Conversely, the skeleton of BP-TEPY is significantly distorted. Its planar conjugation decreases, intersystem crossing (ISC) efficiency increases, which makes it more prone for resonance energy transfer to generate 1O2. Therefore, BP-TEPY displays best photocatalytic activity in [4+2] cycloaddition and thioanisole oxidation. Both above reactant conversion and its product selectivity exceed 99 %. This work systematically reveals the intrinsic structure-activity relationship among the skeleton structure of CPPs, excitonic behavior, and selective generation of ROS, providing new insights for the rational design of highly efficient and selective CPPs photocatalysts.

Bimetallic Mn-Cu oxide catalysts for toluene oxidation: Synergistic effect and catalytic mechanism

A series of Mn-Cu composite oxides with different Mn/Cu molar ratios were synthesized via a facile ethanol-redox precipitation method and investigated for the oxidation of toluene. Among as-synthesized MnxCuy catalysts, Mn5Cu1 showed the most excellent toluene catalytic activity at a weight hourly space velocity (WHSV) of 30000 mL∙g−1∙h−1, with 90 % conversion achieved at 212 °C. Furthermore, the Mn5Cu1 catalyst exhibited exceptional thermal stability over a 12-hour period at 215 °C, along with outstanding resistance to H2O in the range of 5 vol% to 40 vol%. As characterized by XRD, BET, XPS, EPR, H2-TPR, and O2-TPD, it was found that Mn5Cu1 possessed a unique three-phase coexisting structure, large specific surface area (57 m2·g−1), plentiful oxygen vacancies, excellent redox capacity, and strong mobility of oxygen, which were attributable to the synergistic effect between Mn and Cu. This strong synergy between Mn and Cu is the underlying reason for the strong catalytic activity of Mn5Cu1. Moreover, toluene-TPD and TPSR results indicated that appropriate Cu loading was favorable for the adsorption and activation of toluene. The potential reaction pathway for toluene oxidation was presented based on in situ DRIFTS characterization. Maleic anhydride was the critical reaction intermediate species.

Pulsed Laser‐Initiated Dual‐Catalytic Interfaces for Directed Electroreduction of Nitrite to Ammonia

Green and highly selective synthesis of ammonia (NH3) via electrochemical reduction reaction of toxic nitrite (NO2−RR) in a neutral electrolyte is a feasible solution for energy and environmental issues. Dual‐nature electrocatalysts combining metal and metal‐derived materials are crucial for enhancing the selectivity parameter and efficacy of this reaction. Here, Pd‐, Pt‐, Ru‐, and Ir‐decorated Co3(PO4)2 (CoPi) composites with a robust metal–support interaction are obtained via the one‐pot pulsed laser ablation in liquid method. Among the designed composites, Ir–CoPi affords ≈100% Faradaic efficiency, mass balance, and selectivity toward NH3 product at sufficiently low potentials. Further, it affords the highest NH3 yield rate of 19.13 mg h−1 cm−2 with 78.1% removal of toxic NO2− with a rate constant kapp = 0.31 mm min−1 under −1.6 V versus Ag/AgCl. In situ experiments and theoretical investigations reveal the underlying mechanisms responsible for this outstanding performance of Ir–CoPi, which can be accredited to the generation of specific active sites on the Ir component. Insights derived from the evolving intermediate reactive species provide new opportunities for large‐scale NH3 production through electrochemical techniques, density functional theory calculations, and the improvement of the corresponding industrial processes.

Tri-sulfur radical trapping in lithium–sulfur batteries

Lithium-sulfur (Li–S) batteries have emerged as a next-generation battery technology owing to their prospects of high capacity and energy density. They, however, suffer from rapid capacity decay due to the shuttling of reaction intermediate species: Li polysulfides (LiPSs). One of the more important and intriguing PSs is the tri-sulfur radical (S3•−), observed mainly in high-donor number (DN) solvent-based electrolytes. Although this radical has been proposed to be crucial to full active material (AM) utilization, there is currently no direct evidence of the impact of S3•− on cycling stability. To gain more insight into the role of the S3•−, we studied the use of radical traps in low and high DN solvent-based electrolytes by operando Raman spectroscopy. The traps were based on nitrone and iminium cation, and S3•− was indeed successfully trapped in ex situ analysis. However, it was the ionic liquid-based trap, specifically pyridinium, that effectively suppressed S3•− during battery operation. Overall, the PS formation was altered in the presence of the traps and we confirmed the impact of S3•− formation on the Li–S battery redox reactions and show how the trapping correlates with Li–S battery performance. Therefore, stabilization of the S3•− might be a path to improved Li–S batteries.

Ligand-functionalized surfaces for chemoselective heterogeneous catalysis

Selectivity of multi-pathway surface reactions depends on subtle differences in the activation barriers of competing reactive processes, which is difficult to control. One of the most promising strategies to overcome this problem is to introduce a specific selective interaction between the reactant and the catalytically active site, directing the chemical transformations towards the desired route. This interaction can be imposed via functionalization of a solid catalyst with organic ligands, promoting the desired pathway via steric constrain and/or electronic effects. The microscopic-level understanding of the underlying surface processes is an important prerequisite for rational design of such new class of ligand-functionalized catalytic materials. In this perspective, we present an overview over our recent mechanistic studies on heterogeneous Pd(111) catalysts functionalized with different types of organic ligands for chemoselective hydrogenation of a,b-unsaturated aldehyde acrolein. Employing a combination of real space microscopic (STM) and in operando spectroscopic (IRAS) surface sensitive techniques, we show that self-ordered active ligand layers are formed under operational conditions and identify their chemical nature and the geometric arrangement on the surface turning over. Deposition of a ligand layer renders Pd highly active and nearly 100 % selective toward propenol formation by promoting acrolein adsorption in a specific adsorption configuration via the O atom of the C = O bond. In this adsorption configuration, acrolein can be hydrogenated first to the desired reaction intermediate propenoxy species followed by formation of the target product propenol. Both the reaction intermediate and the final product propenol as well as their time evolution were identified by IRAS and gas phase analysis via quadrupole mass spectrometry (QMS). Particular focus of these studies was on the role of geometric and electronic effects imposed by specific functional groups purposefully introduced in the ligand layer. Obtained atomistic-level insights into the formation and dynamic evolution of the active ligand layer under operational conditions as well as into the role of geometric vs. electronic effects imposed by the ligand provide important input required for controlling chemoselectivity by purposeful surface functionalization.

Highly selective oxidation of 3,7-dichloro-8-dichloro methyl quinoline toward quinclorac by CoPc-Mn-Br catalytic system

Nowadays, the use of quinoline derived synthons as precursors of quinclorac products is an important research topic in green chemistry. O2 is a cheap, stable, and eco-friendly oxidant, holding promise for organic oxidation reactions. Herein, we have pioneered the discovery of CoPc-Mn(OAc)2-HBr (CoPc-Mn-Br) catalyst system for the selective oxidation of 3,7-dichloro-8-dichloro methyl quinoline (3,7-D-8-DMQ) into quinclorac with high 3,7-D-8-DMQ conversion at 59.3 %. The CoPc-Mn-Br exhibits excellent selectivity of quinclorac (up to 60.3 %), affording high quinclorac yield of 35.7 %, which is 3.1-fold higher than the yield of Co(OAc)2-Mn(OAc)2-HBr (Co-Mn-Br). Electron paramagnetic resonance (EPR) investigations and density functional theory (DFT) calculations indicate that CoPc promotes the adsorption and activation of O2 in this oxidation process, which generates more Co3+, leading to producing the reactive intermediate species 3,7-dichloro-8-carbonyl quinoline free radicals via the radical process. The insight achieved from this fundamental study may be further applied to other organic syntheses via selective oxidation.

Unravelling the Role of Free Radicals in Photocatalysis.

Free radicals are increasingly recognized as active intermediate reactive species that can participate in various redox processes, significantly influencing the mechanistic pathways of reactions. Numerous researchers have investigated the generation of one or more distinct photogenerated radicals, proposing various hypotheses to explain the reaction mechanisms. Notably, recent research has demonstrated the emergence of photogenerated radicals in innovative processes, including organic chemical reactions and the photocatalytic dissolution of precious metals. To harness the potential of these free radicals more effectively, it is imperative to consolidate and analyze the processes and action modes of these photogenerated radicals. This conceptual paper delves into the latest advancements in understanding the mechanics of photogenerated radicals.

An Easy-to-Use 3D-Printed Electrochemical Cell for I n Situ Raman Spectroscopy

In energy conversion devices such as electrolyzers and batteries, the monitoring of electrode surfaces during electrochemical processes is essential to understand their operation mechanisms. One of the promising techniques is in situ Raman spectroscopy, which can analyze (i) electrode surface structure, (ii) surface species (reaction intermediate species), and (iii) localized electrolyte species.1 The bottleneck for using this technique is the high cost and complexity of commercially available electrochemical cells designed for in situ Raman spectroscopy. To solve these issues, a few research groups provided 3D-printed spectroelectrochemical cells with low cost and less complexity.2,3 However, the spectroelectrochemical cells so far reported require a specific sample type (i.e., particles). We need a low-cost and less-complex spectroelectrochemical cell that can be used for more varieties of samples.In this study, we will provide a new design of a spectroelectrochemical cell that has compatibility with various sample types [i.e., substrates (e.g., metal foil strips, fluorine-doped tin oxide-coated glass, indium tin oxide-coated glass, etc.) and particle]. Specifically, a versatile, low-cost, and less-complex electrochemical cell for in situ Raman spectroscopy will be fabricated using a stereolithography (SLA) 3D printer with resin as a printing material. Herein, using the SLA 3D-printed spectroelectrochemical cell, we will also demonstrate a few example studies for electrolyzer and battery applications. References W. Zheng, Chemistry–Methods, 3, e202200042 (2023).M. F. dos Santos et al., Anal. Chem., 91, 10386–10389 (2019).G. D. da Silveira et al., Anal. Chim. Acta, 1141, 57–62 (2021).

Quantifying defects in carbon nanotubes undergoing prolonged electrochemical cycling with Raman phase map

Electrically conducting graphitic carbon materials are ubiquitous constituents of electrocatalysts and electrochemical energy storage materials. During electrolysis and electrochemical charge-discharge cycles, the carbon matrix is subjected to chemical stress due to drastic changes in the redox environment, the formation of reactive intermediate species and to steric strain caused by intercalation of counter ions. These factors trigger the formation of defects in the graphitic lattice, leading to scattering the charge carriers, thereby reducing the carrier mobility. It is of utmost importance to reliably monitor the graphitic lattice to maintain the integrity of the material and recognize the nature of defects. We have applied statistical Raman measurement technique in conjunction with Raman phase map and Raman ellipse to monitor and quantify the formation of point and line defects in functionalized carbon nanotubes. We also demonstrate how the Raman ellipse in combination with ID/ID′ is a new and powerful analytical tool which can serve to deduce the correct defect generation process in a graphitic lattice exposed to stress during electrochemical cycling. Thus, a deep mechanical insight by “simple” optical spectroscopy can be captured through our proposed Raman phase map analysis.

Understanding the reaction mechanism and kinetics of photocatalytic oxygen evolution on CoOx-loaded bismuth vanadate.

Photocatalytic water splitting for green hydrogen production is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Loading a co-catalyst is essential for accelerating the kinetics, but the detailed reaction mechanism and role of the co-catalyst are still obscure. Here, we focus on cobalt oxide (CoOx) loaded on bismuth vanadate (BiVO4) to investigate the impact of CoOx on the OER mechanism. We employ photoelectrochemical impedance spectroscopy and simultaneous measurements of photoinduced absorption and photocurrent. The reduction of V5+ in BiVO4 promotes the formation of a surface state on CoOx that plays a crucial role in the OER. The third-order reaction rate with respect to photohole charge density indicates that reaction intermediate species accumulate in the surface state through a three-electron oxidation process prior to the rate-determining step. Increasing the excitation light intensity onto the CoOx-loaded anode improves the photoconversion efficiency significantly, suggesting that the OER reaction at dual sites in an amorphous CoOx(OH)y layer dominates over single sites. Therefore, CoOx is directly involved in the OER by providing effective reaction sites, stabilizing reaction intermediates, and improving the charge transfer rate. These insights help advance our understanding of co-catalyst-assisted OER to achieve efficient water splitting.

Modeling Nicotine-Induced Chlorine Loss in Drinking Water Using Updated EPANET-MSX.

Multispecies water quality modeling is critical for simulating complex chemical reactions in drinking water distribution systems. An updated EPANET 2.2-compatible version of EPANET multi-species eXtension (EPANET-MSX) was used, which included dispersion and improved mass balance reporting, to simulate an experimental study. The use of EPANET-MSX was supplemented by an automated Python script to process experimental data, handle model execution, and analyze results. Nicotine-associated chlorine loss in drinking water-initially investigated from a drinking water security perspective-modeled with EPANET-MSX was compared with bottle test and test injection data. Two reaction models were tested (with and without a reactive intermediate), and the model that included a reactive intermediate nicotine species using dispersion was found to produce the best model agreement with experimental data. These results provide a demonstration of the new features within EPANETMSX in the context of the nicotine-chlorine reaction.

Effects of operating temperature on Li-O2 battery with ionic liquid-based binary electrolyte

Awaiting a breakthrough, the Li-oxygen battery (LOB) is considered a promising candidate to meet the high energy demands in the future. Among various critical challenges which hamper its development, the mystery of the electrolyte with optimal properties remains unsolved to this day. In this study, we comprehensively investigated the effects of operating temperature (20C, 40 °C and 60 °C) on the electrochemical performance of LOBs incorporated with room temperature ionic liquid (RTIL) and organic solvent binary electrolyte. We designed and investigated 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][Tf2N]) RTIL and dimethyl sulfoxide (DMSO) organic solvent at various volume ratios ((4:1), (1:1), (1:4)). Among the binary electrolytes, ([C2C1im][Tf2N]/DMSO (1:4)) delivered the highest discharge capacities of 3.70 Ah g− 1 (20 °C), 4.0 Ah g− 1 (40 °C) and 3.65 Ah g− 1 (60 °C) as compared with pure [C2C1im][Tf2N] and DMSO. Cycling stability tests showed superior stability of the binary electrolyte ([C2C1im][Tf2N]/DMSO (1:4)) irrespective of the operating temperature. From viscosity and ionic conductivity measurements (at 20–60 °C), [C2C1im][Tf2N]/DMSO (1:4) exhibited the highest ionic conductivity and the lowest viscosity compared with other binary electrolytes (even with pure electrolytes) at any given temperature. Cyclic voltammetry (CV) tests revealed the highest reaction rates for [C2C1im][Tf2N]/DMSO (1:4) binary electrolytes than pure electrolytes. The superior performance of [C2C1im][Tf2N]/DMSO (1:4) binary electrolyte was ascribed to enhanced stability against reactive intermediate species during oxygen reduction reaction (ORR), increased ionic conductivity, low viscosity (comparable with organic electrolytes), improved oxygen solubility, and relatively low evaporation rates.

Effects of Operating Temperature on Li-O2 Battery with Ionic Liquid-Based Binary Electrolyte

The progress of rechargeable Li-O2 battery (LOB) is hampered due to the number of challenges its components present. Among various critical challenges, the choice of electrolyte has always been a bottleneck impeding the breakthrough in the development of LOB. Various electrolytes, including organic solvents and room-temperature ionic liquids (RTILs) have been developed and studied. Each electrolyte comes with various limitations, which restrict its application in the LOB. These include thermal and electrochemical stability, volatility, viscosity, flammability, capability to dissolve incoming oxygen, diffusivity, and ionic conductivity. Consequently, no electrolyte could be regarded as an ideal electrolyte. Nonetheless, efforts have been made to tune the physiochemical properties of the electrolyte by blending two or more miscible solvents. High thermal and electrochemical stability and negligible volatility of RTILs can be combined with high diffusivity and ionic conductivity of organic solvents by merely blending them with optimized volume ratios.In this study, we comprehensively investigated the effects of operating temperature (20°C, 40°C and 60°C) on the electrochemical performance of LOBs incorporated with RTIL and organic solvent binary electrolyte. We designed and investigated, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][Tf2N]) RTIL and dimethyl sulfoxide (DMSO) organic solvent at various volume ratios ((4:1), (1:1), (1:4)). Among the binary electrolytes, ([C2C1im][Tf2N]/DMSO (1:4)) delivered the highest discharge capacities of 3.70 Ah g-1 (20°C), 4.0 Ah g-1 (40°C) and 3.65 Ah g-1 (60°C) as compared with pure [C2C1im][Tf2N] and DMSO. Cycling stability tests showed superior stability of the binary electrolyte ([C2C1im][Tf2N]/DMSO (1:4)) irrespective of the operating temperature. From viscosity and ionic conductivity measurements (at 20-60°C), [C2C1im][Tf2N]/DMSO (1:4) exhibited the highest ionic conductivity and the lowest viscosity compared with other binary electrolytes and pure RTIL at any given temperature. Cyclic voltammetry (CV) tests revealed a higher reaction rate with [C2C1im][Tf2N]/DMSO (1:4) binary electrolytes than pure electrolytes. The superior performance of [C2C1im][Tf2N]/DMSO (1:4) binary electrolyte was ascribed to enhanced stability against reactive intermediate species during oxygen reduction reaction (ORR), increased ionic conductivity, low viscosity (comparable with organic electrolytes), improved oxygen solubility, and relatively low evaporation rates. The detailed results and discussion will be presented during the presentation.

Insights into the carbon nanotubes-mediated activation of permanganate for decontamination under high salinity

Radical-based advanced oxidation process (AOPs) has attracted great interests in wastewater treatment field. However, by the traditional radical-based method, the degradation of organic pollution is greatly suppressed when radicals react with the co-existing anions in the solution. Herein, an efficient method for degrading of contaminant under high salinity conditions is discussed through a non-radical pathway. Carbon nanotubes (CNTs) was employed as an electron transfer medium to facilitate the electron conversion from contaminants to potassium permanganate (PM). Based the results of quenching experiments, probe experiments, and galvanic oxidation process experiments, the degradation mechanism of CNTs/PM process was demonstrated to be electron transfer, rather than reactive intermediate Mn species. As a result, typical influencing factors including salt concentration, cations, and humic acid have less of an impact on degradation during CNTs/PM processes. In addition, the CNTs/PM system exhibits superior reusability and universality of pollutants, which has the potential to be applied as a non-radical pathway for the purification of contaminant in the large-scale high salinity wastewater treatment.

Application of Co3O4 in Photoelectrocatalytic Treatment of Wastewater Polluted with Organic Compounds: A Review

The negative effects of refractory organic substances in water on the environment and life have aroused worldwide attention. The efficiency of using photoelectrocatalysis (PEC) to degrade refractory organic pollutants depends to a large extent on the properties of the photoanode semiconductor. Therefore, the selection of a satisfactory photoanode semiconductor material to promote the production of intermediate reactive species (hydroxyl radicals and superoxide radicals) has become a key issue in improving the efficiency of PEC. Among the available catalysts, transition metal oxides have received a lot of attention in recent years due to their low price and significant advantages. Due to its outstanding photoelectrocatalytic properties, Co3O4 has emerged as a candidate to serve as a photoelectrocatalyst specifically for the oxidation of water with oxygen in these materials. This paper summarizes in detail the recent advances in Co3O4 materials for PEC, both pure Co3O4 and Co3O4-based composites. In addition, this review discusses the impact of strategies on the performance of photoelectrocatalysts, such as synthesis methods, crystal surface structures, and composites. Finally, this review concludes with a presentation of the challenges and workable solutions for Co3O4-based materials in PEC, along with a discussion of their potential for future research.

Effect of alkaline nitrate addition in the CO2 chemisorption of pentalithium ferrite (Li5FeO4) at low and moderate temperatures

Li, Na and K nitrate-containing pentalithium ferrite (Li5FeO4) samples were prepared to evaluate changes of the CO2 capture process at moderate temperatures. These experiments were performed using different CO2 partial pressures and different characterization techniques, such as TG, DSC, XRD and DRIFTS. When using a CO2 saturated atmosphere, all the samples showed high CO2 capture efficiencies at lower temperatures (150–400 °C) than those observed on the pristine Li5FeO4. Specifically, lithium nitrate-containing samples presented the best CO2 capture properties. Thus, this system was further analysed through in-situ DRIFTS and DSC experiments, elucidating the Li5FeO4-CO2 reaction path. Alkali nitrate salts are melted forming eutectic phases with the carbonate produced, where the first one works as an oxygen donor/acceptor, producing reactive intermediate species improving the CO2 capture. Moreover, at the lowest temperatures, H2O presence plays an important role during the whole CO2 capture mechanism, through the lithium hydroxide formation, enabling the process of CO2 chemisorption. Finally, it was proved that Na and K nitrate-containing samples presented similar behaviours than those described for the lithium case, although CO2 capture temperature regimes were shifted depending on the alkaline nitrate.