Concentration Of CO32 Research Articles

Cutting the cost to combust methane by embellishing the Co-O-Cu interaction in Cu-incorporated Co3O4-based nanocatalysts

Ingredient control brings huge promise for fabricating high-performance Co3O4-based nanomaterials. Herein, for steering the microstructure and properties of Co3O4 system, copper components were incorporated into Co3O4 through a facile coprecipitation ploy taking n-butylamine as the precipitant. At fitting Cu-addition level, dual Co-O-Cu interactions were established by sharing oxygen species, which was based on the partial replacement of Co2+ by Cu2+ in Co3O4 lattice and creation of hetero-interfaces between surface dispersed CuO and Co3O4. Resultly, CH4 combustion efficiency on tailored catalysts was elevated by lessened crystalline sizes, higher dislocation density, preferable capability towards reduction, more abundant Lewis acidic sites, larger surface concentration of Co3+ sites, and the easy regeneration of active surface lattice oxygen contributed from richer O-vacancies. The above optimal attributes-induced supreme activity was accomplished on 0.4Cu-Co3O4 (molar ratio at 0.4), who was revealed to follow MvK CH4 combustion mechanistic model, and to manifest a decent long-term durability in anhydrous condition. Besides, results underscored that Cu-addition presented tiny contribution for water-resistance.

Adjustment mechanism of Co3+ performance in Co3O4-LaOx catalyst for high-efficiency catalytic combustion of toluene

This study employed the sol–gel method to fabricate Co-La catalysts under various calcination temperatures were used to the catalytic oxidation of toluene. The investigation on the impact of calcination temperature on the Co3+ content and the resultant catalytic activity was studied. The CoLa-550 catalyst (calcined at 550 °C) exhibited the highest concentration of Co3+ and optimal catalytic performance for toluene oxidation (T90 = 195 °C). In situ DRIFTS technology confirmed the ring-opening of benzoic acid was the rate-determining step. Comprehensive analyses utilizing XPS, H2-TPR, and O2-TPD revealed the significance of optimizing Co3+ content to enhance catalytic activity. This research provided crucial theoretical and experimental support for the development of efficient non-noble metal catalysts.

Assessing the physicochemical properties of surface/groundwater of Sudhnoti district, Azad Jammu and Kashmir: Impacts on lindane degradation by photocatalysis

Since polluted water deteriorates the health of human beings and other animals, healthy society and environmental sustainability demand for clean and safe water. The presence of contaminants, and imbalance of common physicochemical parameters significantly disturb the quality of water. Taking the importance of clean and safe water into account, this study investigated fourteen physicochemical parameters of hand pump and open well water (main drinking water sources) from fifteen places of district Sudhnoti, Azad Jammu and Kashmir (AJK). The mean values of pH, electrical conductivity (EC), alkalinity, hardness and total dissolved solids (TDS) were 7.6, 349.9 μS/cm, 144, 152 and 190 mg/L, respectively. The mean concentration of Na+, K+, Ca2+, Mg2+, HCO3−, Cl−, SO42− and NO3− was found to be 9.5, 0.96, 9.9, 44.2, 144, 16.8, 8.1 and 6.67 mg/L, respectively. The turbidity as well as the concentration of CO32− was found below the detectable level in all water samples tested. Interestingly, all the studied physicochemical parameters had lower values than the maximum permissible level recommended by the world health organization (WHO) for drinking water. Eventually, the impacts of the studied physicochemical parameters, particularly anions and cation, on the efficiency of water treatment technology for real field application were discussed. The results revealed that physicochemical parameters of the groundwater of Sudhnoti, AJK had a slight effect on the degradation efficiency of one of the most widely used pesticides, lindane, in water by using ultraviolet–visible titanium oxide/hydrogen peroxide (UV–Vis)/TiO2/H2O2) and ultraviolet–visible/titanium oxide persulfate photocatalysis. Of note, the quality of hand pump and open well water which are the main drinking water sources of district Sudhnoti, AJK was found to be fit for drinking and other domestic purposes as well as for the ecosystem.

Valence study of Li(Ni0.5Mn0.5)1−xCoxO2 and LiNi1−xCoxO2 : The role of charge transfer and charge disproportionation

The series of LiMO2 (M: transition metal) materials are highly relevant as cathode materials of Li-ion batteries. The stability of such systems remains an important factor for their usability in batteries, and depends strongly on the electronic configuration of the transition-metal ions. In particular, the promising class of multi-transition-metal systems exhibits complicated valence states due to intermetallic charge transfer and charge disproportionation. Here we perform a systematic study on the valence of the transition-metal ions using x-ray absorption spectroscopy on the M−L2,3 edges and O-K edges. In Li(Ni0.5Mn0.5)1−xCoxO2 we established that the valence is Co3+ and Ni0.52+Mn0.54+ throughout the whole series. Meanwhile, in LiNi1−xCoxO2 we found that the Ni displays a behavior consistent with a charge disproportionated negative charge transfer system, and that with increased concentration of Co3+, the disproportionation signal decreases. Since the number of O 2p holes also gets reduced, we infer that the material will also become more unstable. Published by the American Physical Society 2024

Electrocatalytic Activities of High-Entropy Oxides for the Oxygen Evolution Reaction

Electrocatalytic water-splitting hydrogen generation consists of the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER), where the four-electron-relevant OER is the rate-determining step. So far, there have been many efforts to substitute for the highly expensive noble-metal electrocatalysts (platinum, ruthenium or rhodium oxides, etc.). Transition-metal oxides based on Co, Ni, Mn, and V have been suggested as such alternatives, due to their low cost, high efficiency, and high stability. Recently, since the compositional diversity can provide a new breakthrough in that area, a high-entropy oxide (HEO) with five transition-metal cations has been suggested as a promising electrocatalyst toward the OER. In our studies, two kinds of HEOs were prepared and their OER activities were investigated. To begin with, for the (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)O, the effect of constituent cations on the OER activity was unveiled. Furthermore, a core cation driving the high OER activity was found. For it, the medium-entropy oxides (MEOs) with four cations are prepared by subtracting each cation (Mg, Fe, Co, Ni, or Cu) from the HEO, exhibiting homogeneous morphology, equiatomic composition, and single-phase rocksalt structure. As a result, it is found that the highest concentration of Co3+ in the MEO (w/o Cu) leads to the best OER activity, and thus Co3+ is the core ion driving the high OER activity. Furthermore, it is regarded that Cu2+ ions prevent the conversion of Co or Fe cations from 2+ to 3+ in the HEO and MEOs. Accordingly, maximizing the concentration of Co3+ within electrocatalysts is suggested as an effective design strategy for the high-efficiency electrocatalysts based on high or medium entropy materials. Secondly, the relationship between structure and OER activity was elucidated for the (Mg0.2Fe0.2Co0.2Zn0.2Cu0.2)O with a temperature-dependent rocksalt-to-spinel transition.

Design Sr, Mn-doped 3DOM LaCoO3 perovskite catalysts with excellent SO2 resistance for benzene catalytic combustion

Anti SO2 poisoning is a major scientific challenge in the field of VOCs catalytic combustion. To enhance sulfur resistance of 3DOM LaCoO3 perovskite catalysts, the strontium (Sr) and manganese (Mn) elements were doped to regulate and control its microstructure and electronic valence states of active metals. The macropore structure is constructed to accelerate the adsorption and diffusion of benzene and intermediate species and promote the deep oxidation in ordered macropores. Surprisingly, we observed that the co-doping of Sr and Mn components resulted in the superior catalytic performance for benzene catalytic combustion. Especially, the sulfur resistance of LaCoO3 catalyst was significantly improved due to the doping of Sr and Mn species. Through various characterizations, it is discovered that the doping of Mn component in 3DOM LaCoO3 perovskite catalyst could promote the formation of active Co3+ species due to the excellent redox properties between Mn&+ and Co&+ species (Mn4++Co2+→Mn3++Co3+), while the co-doping of Sr and Mn elements could produce and form some new active species. On one hand, Sr and Mn may act as an electron promoter to increase the concentration of Co3+ and Oads. On the other hand, Sr and Mn can act as a structure promoter to enhance the specific surface area and promote the dispersion of active Co species. The research provides valuable reference for the development of highly efficient catalysts for the industrial degradation of benzene.

Study of the Euphrates River’s Water Quality in Front of and Behind the Haditha Dam in Anbar Province, Iraq

Contaminants in natural water continue to be one of the largest environmental issues on the planet. This is due to the fact that due to population expansion, urbanization, agricultural practices, and industrialization, there is a significant increase in the demand for freshwater and a water crisis in arid and semi-arid areas. The present study aimed to assess the suitability of water quality at Haditha Dam. In this study, 9 parameters, including Nitrate NO3, Carbonate CO3, bicarbonate HCO3, Sulphate SO4, Chloride Cl, Calcium Ca, Magnesium Mg, Sodium Na, and Potassium K were measured and investigated to assess water quality for Haditha Dam Project in both sides (Behind and in front of the dam). The current study focuses on the examination of water quality data collected over a one-year period from both sides of the Euphrates River through the collection of 48 samples. The parameters that were examined used the accepted techniques. Findings showed that average concentrations were lowest during the dry season and highest during the rainy season for K, Ca, Na, Mg, Cl, and SO4. However, HCO3 and CO3 concentrations were the highest averages in the dry season, while the lowest average was in the wet season. The results were compared with Iraqi standards for water quality and the World Health Organization (WHO). The planning and logical management of water resources, including the possibility of using them for irrigation and drinking water, can benefit from this study. According to the findings, river water is deemed unsafe for drinking and human consumption, however it can be utilized for irrigation.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Machine Learning Surrogates of a Fuel Matrix Degradation Process Model for Performance Assessment of a Nuclear Waste Repository

Spent nuclear fuel repository simulations are currently not able to incorporate detailed fuel matrix degradation (FMD) process models due to their computational cost, especially when large numbers of waste packages breach. The current paper uses machine learning to develop artificial neural network and k-nearest neighbor regression surrogate models that approximate the detailed FMD process model while being computationally much faster to evaluate. Using fuel cask temperature, dose rate, and the environmental concentrations of CO3 2−, O2, Fe2+, and H2 as inputs, these surrogates show good agreement with the FMD process model predictions of the UO2 degradation rate for conditions within the range of the training data. A demonstration in a full-scale shale repository reference case simulation shows that the incorporation of the surrogate models captures local and temporal environmental effects on fuel degradation rates while retaining good computational efficiency.

Study on failure mechanism on rechargeable alkaline zinc-Air battery during charge/discharge cycles at different depths of discharge.

Background: Zinc-air battery (ZAB) is a promising candidate for energy storage, but the short cycle life severely restricts the wider practical applications. Up to date, no consensus on the dominant factors affecting ZABs cycle life was reached to help understanding how to prolong the ZAB's cycle life. Here, a series of replacement experiments based on the ZAB were conducted to confirm the pivotal factors that influence the cycle life at different depths of discharge (DOD). Method: The morphology and composition of the components of the battery were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and chemical titration analyses. Result: SEM images and XRD results revealed that the failure of the zinc anode gradually deepens with the increase of DOD, while the performance degradation of the tricobalt tetroxide/Carbon Black (Co3O4/CB) air cathode depends on the operating time. The concentration of CO3 2- depends on the charge/discharge cycle time. The replacement experiments results show that the dominant factors affecting the ZAB's cycle life is the reduction of active sites on the surface of Co3O4/CB air cathode at a shallow DOD, while that is the carbonation of the electrolyte at a deep DOD. The reduction of active sites on the surface of Co3O4/CB air cathode is caused by the coverage of K2CO3 precipitated by carbonation of the electrolyte, suggesting that the carbonation of the alkaline electrolyte limits ZAB's cycle life. Conclusion: Therefore, this work not only further discloses the failure mechanism of ZAB, but also provides some feasible guidance to design a ZAB with along cycle life.

Optimization of Ascorbic Acid in the Synthesis of Cobalt Oxide for Enhanced Electrocatalytic Activity toward the Oxygen Evolution Reaction

In this work, we are reporting the combustion synthesis of Co3O4 nanoparticles (NPs) and investigation of the influence of the oxidizing agent [Co(NO3)2] and fuel content (ascorbic acid) on the microstructural and electrochemical characteristics of the NPs. Co3O4 NPs were prepared by varying the relative amount of cobalt nitrate to ascorbic acid in ratios of 1:0.5, 1:1, 1:2, and 1:4, and labeled as S1, S2, S3, and S4 respectively. X-ray diffraction data confirm the formation of the cubic phase of Co3O4, and transmission electron micrographs reveal the formation of fairly dispersed particles in the cases of samples S1 and S2 with average particle sizes of 24.5 ± 3.6 and 20.4 ± 1.2 nm and polydispersity indices of 14.7 and 6.5%, respectively. The X-ray photoelectron spectroscopy analysis reveals that the concentration of Co3+ ions at the surface of Co3O4 NPs increases from sample S1 to sample S2 and thereafter decreases in the case of samples S2 to S3, and S4. On the other hand, the oxygen vacancy decreases with an increase in the ascorbic acid content, that is, from sample S1 to sample S4, the oxygen vacancy decreases. Sample S1 having a high oxygen vacancy with low Co3+ possesses a low activity due to the decrease in conductivity caused by excess oxygen vacancies. Further, samples S3 and S4 showed low activity due to the low oxygen vacancy and low Co3+ content, having a low electrochemical surface area. Finally, sample S2 having the optimum oxygen vacancy with the highest Co3+ content showed the highest activity due to the high conductivity and the highest electrochemical surface area. The Tafel slope for sample S2 is found to be 54.46 mV/dec, denoting the highest activity. The electrochemical impedance analysis revealed that sample S2 exhibits the lowest polarization resistance during the oxygen evolution reaction test, showing enhanced kinetics for the oxygen evolution reaction.

In situ decoration of Co3O4 on N-doped hollow carbon sphere as an effective bifunctional oxygen electrocatalyst for oxygen evolution and oxygen reduction reactions

Transition metal oxide based materials are believed as a sustainable and effective electrocatalysts for oxygen evolution and oxygen reduction reactions (OER/ORR). However, poor conductivity, specific surface area, and tunable crystallography are major bottlenecks. To alleviate such issues, we developed a highly active spinel Co3O4 decorated N-doped hollow carbon sphere (Co3O4/NHCS) by single step decoration using cobalt phthalocyanine (CoPc) precursor for the first time. The introduction of various extents of CoPc significantly affects the sphere wall thickness, defect sites, doping amount of cobalt content, and the concentration of Co3+ and Co2+ sites. The resulting optimum loading of 0.2 g of Co3O4/NHCS-0.2, exhibits a highly uniform hollow carbon sphere with a high wall thickness (61 nm), better surface area (445 m2 g−1), and moderate defect sites. Notably, an exterior concentration of octahedral Co3+ (35.50%) and tetrahedral Co2+ (26.54%) sites serve as the active centres for OER and ORR, respectively. Remarkably, the obtained material exhibits exceptional OER performance with a potential of 1.80 V vs. RHE in 0.1 M KOH medium for achieving a current density of 10 mA cm−2, outperforming the benchmark RuO2 material. In addition, Co3O4/NHCS-0.2 demonstrates an impressive ORR electrocatalytic activity with onset potential of 0.89 V vs. RHE, excellent current density of 5.0 mA cm−2, lower Tafel slope of 60 mV dec−1 and close to four electron transfer. Moreover, the moderate carrier concentration, flat band potential, higher tetrahedral Co2+ and pyridinic N sites significantly improved the ORR activity and methanol oxidation tolerance ability.

Facile preparation and efficient MnxCoy porous nanosheets for the sustainable catalytic process of soot

The pursuit of high-performance is worth considerable effort in catalysis for energy efficiency and environmental sustainability. To develop redox catalysts with superior performance for soot combustion, a series of MnxCoy oxides were synthesized using MgO template substitution. This method greatly improves the preparation and catalytic efficiency and is more in line with the current theme of green catalysts and sustainable development. The resulting Mn1Co2.3 has a strong activation capability of gaseous oxygen due to a high concentration of Co3+ and Mn3+. The Mn doping enhanced the intrinsic activity by prompting oxygen vacancy formation and gaseous oxygen adsorption. The nanosheet morphology with abundant mesoporous significantly increased the solid–solid contact efficiency and improved the adsorption capability of gaseous reactants. The novel design of Mn1Co2.3 oxide enhanced its catalytic performance through a synergistic effect of Mn doping and the porous nanosheet morphology, showing significant potential for the preparation of high-performance soot combustion catalysts.

Removal of methylisothiazolinone biocide from wastewater by VUV/UV advanced oxidation process: Kinetics, mechanisms and toxicity

Methylisothiazolinone (MIT) is frequently used as antimicrobial in household and industrial products, and poses ecological and health risks to aquatic organisms and humans. In this study, vacuum ultraviolet (VUV)/ultraviolet (UV) irradiation was found highly efficient for removal of MIT. The rate constant of MIT degradation (kobs) under VUV/UV irradiation was 3.75 μEinstein−1 cm2, which was around 12.5 times higher than that under UV irradiation. The •OH concentration during the VUV/UV process was 1.0 × 10−12 M. The contributions of UV photolysis and •OH oxidation to MIT degradation under VUV/UV irradiation were 7.3% and 92.7%, respectively. The optimum solution pH (6.0–7.1) gave kobs 33%–39% higher than those at pH 3.9 and 9.3. CO32−/HCO3− inhibited MIT degradation and the kobs decreased by 74% when the concentration of CO32−/HCO3− was increased to 1 mM. The order of MIT removal efficiency under VUV/UV irradiation was ultrapure water > secondary effluent > reverse osmosis (RO) concentrate, because of the light screening and •OH quenching effect of actual wastewater. In RO concentrate, the rate constant of MIT degradation under VUV/UV irradiation was 22% higher than that obtained under UV irradiation. The reduction of TOC, UV254, and total fluorescence regional integration of the RO concentrate during VUV/UV process were 7.2%, 34.9%, and 52.3%, respectively. Twelve main transformation products of MIT were identified after VUV/UV degradation. The main degradation mechanisms of MIT were sulfur atom oxidation and hydroxyl addition. Quantitative structure–activity relationship analysis showed that VUV/UV degradation was an efficient method to remove the toxicity of MIT.

Enhanced improvement of soda saline-alkali soil by in-situ formation of super-stable mineralization structure based on CaFe layered double hydroxide and its large-scale application

In-situ super-stable mineralization technology with mineralizers (CaSO4, Fe2(SO4)3) and attapulgite (ATP) clay were applied to improve soda saline-alkali soil. The addition of mineralizers and the existence of OH and CO32− in soil resulted in the formation of CaFe-layered double hydroxide (CaFe-LDH) with super-stable mineralization structure (Ksp = 1.512 × 10−61), which was confirmed by the characterization of physicochemical properties and density functional theory (DFT) calculation. The fixation of OH− and CO32− during the formation process of CaFe-LDH led to the transformation of the existing forms of OH− and CO32− in soil from free to stable state, resulting in the permanent decrease of soil pH and CO32− concentration. The effect of ATP clay on the decrease of soluble Na ions in soil through electrostatic attraction and cation exchange was also indicated. Furthermore, mineralizers (1.2 t/ha CaSO4 and 0.75 t/ha Fe2(SO4)3) and ATP clay (1.2 t/ha) were applied to 1.33 ha soda saline-alkali land, and Rumex patientia L. was seeded meanwhile for the identification of improved performance. After five months of improvement, the physical and chemical properties of soil were improved that pH, electrical conductivity (EC), the concentration of CO32− and soluble Na ions, and soil bulk density decreased significantly. In addition, the emergence rate of Rumex patientia L. increased from 0% to 98.3%. All above indicated that in-situ super-stable mineralization technology with the properties of high efficiency, long-term and cost-effective (234.88 $/ha) displays excellent potential in the improvement of soda saline-alkali soil.

Degradation of contaminants of emerging concern in UV/Sodium percarbonate Process: Kinetic understanding of carbonate radical and energy consumption evaluation

UV/sodium percarbonate (UV/SPC) advanced oxidation process is an efficient and green technology to remove contaminants of emerging concern (CECs), with the simultaneous formation of hydroxyl radical (•OH) and carbonate radical (CO3•−). This study investigated the degradation of eight CECs in UV/SPC process, including phenol, atrazine, bisphenol A, ibuprofen, sulfadiazine, acetaminophen, carbamazepine, and diuron. A model was established to simulate the experimental results, which shows that both •OH and CO3•− played crucial roles in UV/SPC process, and the steady-state concentrations of CO3•− were much higher than that of •OH. The higher concentration compensates for the low reactivity of CO3•− with CECs and the loss of •OH depleting by CO3•−. Also, the Hammett constants decreased linearly with increasing natural logarithms of rate constants, indicating the selectivity of CO3•− with electron-donating substituents. In real water, CEC degradation was significantly inhibited due to the competition for light absorption from background compounds and scavenging of free radicals, especially CO3•−, by water matrix. Further, demethylation, decarbonylation, hydroxylation, amino oxidation, and quinonization were proposed as the main reactions for CEC degradation in UV/SPC process. The minimum electrical energy per order (EE/O) was calculated as 0.152 kWh m−3, with SPC dose of 0.138 mM and UV intensity of 2.02 × 10-7 Einstein L−1 s−1.

Highly active urchin-like MCo2O4 (M = Co, Cu, Ni or Zn) spinel for toluene catalytic combustion

MCo2O4 (M = Co, Cu, Ni or Zn) spinel catalysts have been prepared using a chemical co-precipitation method and applied in toluene combustion. The physicochemical properties of the MCo2O4 catalysts was discussed to explore the impact of substitution on the tetrahedral A-site ions. The results of the activity evaluation show that the catalytic performances of Co3O4, CuCo2O4 and NiCo2O4 with urchin-like morphology are far superior than ZnCo2O4 nanoparticles. The CuCo2O4 catalyst exhibited the mostsuperior performance for toluene combustion, and the toluene conversion rate reached 90% at 230 °C. When compared to the other catalysts, the optimal activity of CuCo2O4 was attributed to the presence of more reactive oxygen species, a higher concentration of Co3+ ions on catalyst surface and better reducibility at relative lower temperature. Moreover, the catalytic activity of the CuCo2O4 catalyst did not decrease significantly in the long-term test, demonstrating its excellent stability.

Water quality in the central zone of the Texcoco aquifer, Mexico

Objective: To determine water quality in the central zone of the Texcoco aquifer, Mexico, for human use and consumption and agricultural use. Methodology: The physical, chemical, and biological indicators of the water from 16 wells in urban areas of the central zone of the aquifer were determined. The sampling was carried out, based on the parameters and definition of water quality per use established in the current official Mexican standards. Results: According to the physical indicators and concentrations of CO32-, HCO3-, Ca2+, Mg2+, Cl-, SO42-, PO43-, Na+, K+, Fe, Cu, and Zn, the water in the sample was suitable for human use and consumption and agricultural use. Based on the cadmium (Cd) concentration, the water was unsuitable for human use and consumption and agricultural use, in 12 and 6 wells, respectively. According to the lead (Pb) concentration, water was suitable for agricultural use in the 16 wells studied; however, it was unsuitable for human use and consumption in any of the wells. In eight wells analyzed, the presence of fecal coliforms was lower than the permissible limit for agricultural use. Implications: This study complements researches done in other areas of the aquifer. The causes of water pollution are unknown and researches about the vulnerability of the aquifer and the possible polluting sources should be carried out. Conclusions: The water from the aquifer in the central zone has limitations for human use and consumption and agricultural use, as a consequence of the high Cd and Pb concentrations and its microbiological quality.

The reuse of nano-TiO2 under different concentration of CO32– using coagulation process and its photocatalytic ability in treatment of methyl orange

• Al-based coagulants can effectively separate nano-TiO 2 . • Flocs formed by different coagulants can degrade methyl orange. • AT 2 achieved high degradation efficiency under UV irradiation. • It proposes a new perspective on recycling coagulated flocs for sewage treatment. Photocatalysis is highly efficient for the treatment of dyeing wastewater. However, the wastewater still contains a large amount of nano-TiO 2 after photocatalysis. In order to reduce the cost of nano-TiO 2 , different coagulants were used to improve the solid/liquid separation efficiency. At the same time, the reuse of flocs has raised increasing attention after coagulation. In this study, we report on the recycling of flocs for the production of AlCl 3 and TiO 2 formed flocs (AT 1 ) and Al 13 and TiO 2 formed flocs (AT 2 ) through a simple calcination process. Results indicated the flocs formation processes under different concentration of CO 3 2– were Al species distribution and coagulant dosage dependent. Without HA molecules, the reaction between Al-based coagulants and CO 3 2– are the controlling steps in the coagulation process, and Al a and Al b species had different reaction processes. The influence of HA molecules was also studied, and the HA-Al aggregates which could bridge the TiO 2 nanoparticles, and thus induce sweep flocculation. Consequently, highly enhanced aggregation rate, due to the heteroaggregation between these aggregates and TiO 2 was observed. After calcination, the AT 2 -10 and AT 2 -20 (CO 3 2– : 10, 20 mmol/L) with petal-like structures (mesoporous), relatively high specific surface areas, i.e. 83.98 m 2 /g and 78.38 m 2 /g and high photocatalytic degradation, i.e. 72.79%, 67.78% (compared to nano-TiO 2 , AT 1 -10 and AT 1 -20), were obtained. Additionally, oxygen vacancy (OV) was generated on the surface of the recycled AT 2 -10 and AT 2 -20, which display strong photocatalytic performance for the degradation of MO greater than 65%, under ultraviolet (UV) irradiation and without any sacrificial reagents. This study proposes a new perspective on recycling coagulated flocs for practical application in wastewater treatment.

Correlative operando microscopy of oxygen evolution electrocatalysts

Transition metal (oxy)hydroxides are promising electrocatalysts for the oxygen evolution reaction1-3. The properties of these materials evolve dynamically and heterogeneously4 with applied voltage through ion insertion redox reactions, converting materials that are inactive under open circuit conditions into active electrocatalysts during operation5. The catalytic state is thus inherently far from equilibrium, which complicates its direct observation. Here, using a suite of correlative operando scanning probe and X-ray microscopy techniques, we establish a link between the oxygen evolution activity and the local operational chemical, physical and electronic nanoscale structure of single-crystalline β-Co(OH)2 platelet particles. At pre-catalytic voltages, the particles swell to form an α-CoO2H1.5·0.5H2O-like structure-produced through hydroxide intercalation-in which the oxidation state of cobalt is +2.5. Upon increasing the voltage to drive oxygen evolution, interlayer water and protons de-intercalate to form contracted β-CoOOH particles that contain Co3+ species. Although these transformations manifest heterogeneously through the bulk of the particles, the electrochemical current is primarily restricted to their edge facets. The observed Tafel behaviour is correlated with the local concentration of Co3+ at these reactive edge sites, demonstrating the link between bulk ion-insertion and surface catalytic activity.