Reaction Kinetics Research Articles

CO2 treatment of recycled concrete aggregates with high mortar contents: From finding optimal treatment condition, quality enhancement, to life cycle assessment

With increasing construction and demolition waste, the demand for recycled concrete aggregates (RCA) has risen, yet their inherent poor-quality limits usage. In response, CO2 treatment has been developed to enhance RCA quality while contributing to CO2 reduction efforts. This study investigates the effect of CO2 treatment on RCA with high mortar contents for sustainable construction applications. Treatment conditions were optimized by evaluating the CO2 consumption ratio and reaction kinetics under various temperatures (10–50°C), pressures (250–1000 kPa), relative humidity (30–70 %), and initial saturation (30–100 %). X-ray imaging confirms carbonation within the mortar, evidenced by increased greyvalues. Environmental assessment of leachate reveals a significant reduction in chromium concentration from 0.18 mg/L to 0.11 mg/L and a decrease in pH from 10.1 to 7.8 after CO2 treatment, suggesting the potential of CO2 conditioning to mitigate the environmental impacts. Mechanical tests, the aggregate crushing value (ACV) test, and the freeze-thaw (FT) resistance test, demonstrate the improved resistance and durability, with a decrease in ACV from 35.5 % to 33.2 % and FT mass loss from 25.1 % to 20.0 %. The life cycle assessment analysis shows that a simplified CO2 treatment achieved a significant reduction of 138.257 kg CO2 eq per ton of RCA compared to the conventional RCA process. These findings highlight the dual benefits of CO2 treatment: enhanced mechanical performance and reduced environmental impact, promoting the use of recycled aggregates in sustainable construction practices.

Bi-doped initiates the crystal structure reconfiguration of Aurivillius, boosts piezoelectric response, and achieve PMS activation and antibiotic degradation in Bi2LaNbTiO9-BiOBr heterojunctions

Piezo-photocatalysis has been widely accepted as a research strategy for environmental treatment. However, the outstanding issues of synergistic pressure response and charge transfer are still the difficulties in this area, so it is crucial to improve these points. Doping modification of piezoelectric materials is a well-established method to enhance the piezoelectric response and promote charge transfer by modulating the crystal structure. In this study, the crystal structure of Bi4Ti3O12 has been reconstructed by double doping substitution at A and B sites, which realizes the layer change of perovskite structure and the structural distortion of MO6 (M = Ti, Nb). This change in crystal symmetry effectively enhances the piezoelectric response of the material and combined with the construction of Bi2LaNbTiO9-BiOBr (BLNT-BOB) heterojunctions, the charge distribution is dramatically improved, and the charge transfer becomes easier. Under the dual effect of heterojunction and piezo-photocatalytic coupling, the catalyst exhibited excellent catalytic performance, and the degradation rate of BhB reached 97.24 % within 20 min, After PMS activation, the degradation rate reached 98.65 % in 16 min, which was higher than that of BLNT (59.13 %) and BOB (46.81 %), and the reaction kinetics were improved by 5.3-fold and 7.4-fold. It also showed good degradation efficiency in the treatment of antibiotics, and the soybean sprout culture experiment provided a strong proof of the applicability of the catalyst in multiple pollutants and biocompatibility. This work provides valuable insights for designing piezoelectric photocatalytic structures and analyzing the activation mechanism of PMS.

Effect of Catalyst Concentration on Reaction Rate in Organic Synthesis in Kenya

Purpose: The aim of the study was to assess the effect of catalyst concentration on reaction rate in organic synthesis in Kenya. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low-cost advantage as compared to field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: Increased catalyst concentration typically enhances the reaction rate by providing more active sites for the reactants to interact, thereby accelerating the reaction process. This phenomenon follows the principles of collision theory, which states that a higher concentration of catalyst molecules leads to more frequent collisions with reactant molecules, thus increasing the likelihood of successful reactions. Studies have shown that in many organic syntheses, an optimal catalyst concentration exists where the reaction rate is maximized; beyond this point, further increases in catalyst concentration may result in negligible improvements or even adverse effects due to catalyst aggregation or inhibition. Additionally, the nature of the catalyst, its dispersion in the reaction medium, and the specific reaction mechanism all play significant roles in determining the overall impact of catalyst concentration on reaction kinetics. Consequently, fine-tuning the catalyst concentration is essential for optimizing reaction conditions, improving yields, and achieving desired product selectivity in organic synthesis. Implications to Theory, Practice and Policy: Transition state theory, collision theory and michaelis menten kinetics may be used to anchor future studies on assessing effect of catalyst concentration on reaction rate in organic synthesis in Kenya. Practical guidelines are crucial for optimizing catalyst concentration in specific reaction types and industrial settings. Establishing regulatory frameworks that incentivize efficient catalyst concentration practices within industries is imperative.

Photodegradation of Methylene Blue Dye Using BiVO₄/g-C₃N₄ Composites under Visible Light Irradiation

This study evaluates the degradation of methylene blue through photocatalysis using BiVO4/g-C3N4 material with the help of visible light. Material characterization was conducted using X-ray diffraction, scanning electron microscopy, and UV-Vis diffuse reflectance spectroscopy data. The characterization results show that the crystal structure of BiVO4/g-C3N4 is a heterojunction between monoclinic BiVO4 and hexagonal g-C3N4, with a crystal size of about 10.16 nm and a band gap energy value of about 2.16 eV. The morphology formed is a combination of sheet and rod-like. This study optimized the photocatalytic activity of the composite by analyzing the variation of g-C3N4 concentration, degradation time, and methylene blue pH. The results show that the BiVO4/g-C3N4 sample has optimal photocatalytic and adsorption properties in sample B (1:3) with pH 7 and a degradation time of 150 minutes. Under these conditions, the BiVO4/g-C3N4 composite successfully degraded methylene blue by 94.14%. The rate kinetics of the photocatalytic reaction followed first order, with *OH species playing the most role in the degradation mechanism. These findings highlight the potential of BiVO4/g-C3N4 as an effective photocatalyst material for organic pollutant degradation applications, offering a sustainable solution for wastewater treatment.

Controllable Synthesis of Magnetic Composite Derived from MIL-88D and Study on Adsorption Properties of Cu2+

In this paper, MIL-88D (Fe) with spindle shape was prepared by the hydrothermal synthesis method, a metal oxide with a new structure was obtained by calcination at different temperatures as a precursor, and a magnetic iron oxide composite was prepared successfully. At the same time, it was used as an adsorption material for the adsorption of heavy metal ions Cu2+. The influence of the initial pH value and adsorption time on the adsorption effect was investigated, the adsorption kinetics and adsorption isotherm were further fitted, and the adsorption mechanism was preliminarily analyzed. The results show that the magnetic iron oxide composites have a good adsorption capacity for Cu2+. The pH value is an important parameter that affects the adsorption effect. The adsorption of Cu2+ by magnetic iron oxide composites reached adsorption equilibrium in 30 min. The adsorption of Cu2+ by magnetic iron oxide composites conforms to the second-order reaction kinetics and Langmuir adsorption isotherm equation, which indicates that the adsorption process mainly occurs through chemisorption and typical single-molecular-layer adsorption.

Role of Nanoparticle Size in the Photocatalytic Degradation of Pollutants

Purpose: The aim of the study was to assess the role of nanoparticle size in the photocatalytic degradation of pollutants. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low cost advantage as compared to a field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: The study indicated that smaller nanoparticles exhibit a higher surface area-to-volume ratio, providing more active sites for pollutant interaction and adsorption, which enhances the overall degradation process. Additionally, smaller nanoparticles tend to have higher charge carrier mobility and reduced recombination rates of electron-hole pairs, further improving photocatalytic activity. This increased efficiency is critical in environmental applications, as it allows for the effective breakdown of various contaminants, including dyes, pesticides, and pharmaceuticals, at lower catalyst loadings and shorter reaction times. The optimization of nanoparticle size, therefore, plays a crucial role in developing advanced photocatalytic systems for environmental remediation. Implications to Theory, Practice and Policy: Optical absorption theory, surface area and reaction kinetics theory and charge carrier dynamics theory may be used to anchor future studies on assessing the role of nanoparticle size in the photocatalytic degradation of pollutants. Develop robust methodologies for synthesizing nanoparticles with precise control over size distribution. Establish standardized protocols for evaluating the performance and safety of nanoparticle-based photocatalytic materials. This includes setting benchmarks for degradation efficiency, durability, and potential environmental impacts.

Simply fabricating F-doped V2O3 nanoparticles adhered to N-doped carbon as a high-rate anode

The development and application of V2O3-based anodes are hindered by their poor reversible capacity and rate performance. Doping F and combined with N-doped carbon at the same time would achieve excellent electrochemical performance, but the related materials are not prepared and employed to lithium-ion batteries due to the absent synthetic method. In this investigation, a simple strategy was firstly invented to achieve F-doped V2O3/N-doped carbon composite. The F-doped V2O3 nanoparticles are adhered to N-doped carbon, which would enhance electrochemical reaction kinetics. As a result, a high capacity of 481 mAh/g can be obtained at 2 A/g.

Chemical effect of H2 on NH3 combustion in an O2 environment via molecular dynamics simulations

Due to the imperative to reduce carbon emissions, NH3-H2 mixed combustion has garnered significant attention. However, the knowledge of the reaction kinetics of NH3-H2-O2 mixtures at the molecular level remains limited. In this paper, the reactive force-field (ReaxFF) method was employed to study the microscale reaction kinetics of the NH3-H2-O2 mixture with varying hydrogen ratios (HR). The results of the microcanonical ensemble simulations indicated that the addition of H2 significantly increased the combustion performance of NH3. However, H2 did not change the two primary reaction paths of NH3 oxidation (NH3 → N2H2 → N2 and NH3 → NO → N2). The addition H2 not only led to a shift in the initiation reactions from NH3-O2 to H2-O2 reactions, but also notably enhanced the concentration of HO2 and OH radicals (e.g., O2 + H2 → HO2 + H), which accelerated the extraction of H from NxHy and subsequently facilitated the immediate formation of N2. Furthermore, the ignition delay decreased from 120 ps to 40 ps, and the activation energies decreased from 295.46 kJ/mol to 162.12 kJ/mol as HR increased from 0 to 0.3 under the equivalence ratio of 0.4. These key findings can guide the development of clean NH₃ combustion technology.

Facilely tuning the triazine-heptazine ratios in crystalline g-C3N4 for efficient photo-degradation of tylosin

Intrinsically, g-C3N4 has high-density defects, insufficient efficiencies of photogenerated charge carrier separation and transfer, and inadequate photocatalytic ability against antibiotics. A facile crystallinity engineering on g-C3N4 assisted by molten-salts and simultaneously fine-tuning the triazine-heptazine ratio led to forming type-II homojunctions, without introducing foreign atoms and being metal-free. It was successfully achieved through modulating the calcination temperatures and using KCl-LiCl. The salts accelerated deamination reaction kinetics, tuned the unit ratio, and improved the degree of carbon nitride polymerization. At a triazine-heptazine ratio of 74:26 obtained at 450 °C, 10 mg/L of tylosin was completely mitigated within 9 min by the catalyst. Active radicals including O2− and OH were boosted from charge carriers under visible light, and the recombination of photogenerated excitons was relieved on the interfaces of the homojunctions. Breaking glycosidic bonds and dropping off deoxyglycosyl moieties are considered the main degradation mechanism. The cytotoxicity and acute toxicity of the degradation product are classified as harmless. In addition, 3D-molecular docking between the transformation products and target proteins (L4 and L22) in ribosome confirms toxicity reduction. This work paves a way for efficient and harmless photocatalytic degradation of tylosin by facilely modulating the unit ratio and enhancing the crystallinity of carbon nitride without introducing foreign atoms.

Ab initio chemical kinetics and shock-tube experimental study on nitrocyclohexane pyrolysis and combustion

Nitrocyclohexane (NCH) is a model nitroalkane compound with naphthenic structural groups for studying the combustion properties of nitro-based energetic fuels, and also demonstrates significant potential applications for advanced engines. However, accurate description of the detailed kinetic mechanisms for pyrolysis and combustion of NCH receives little attentions. Herein, the detailed pyrolysis and oxidation mechanism of NCH is studied by using quantum chemistry calculations and chemical kinetic theory. The potential energy surfaces of the CN bond dissociation reaction, HONO elimination reaction, abstraction reactions of NCH as well as the subsequent β-scission reactions are calculated using G4//M06–2X/6–311++G(d, p) method, which are subsequently employed for reaction rate constant computations via transition state theory (TST) and RRKM/master-equation (RRKM/ME) method. The ab initio chemical kinetic study results are used to develop a detailed kinetic mechanism to predict the pyrolysis experimental results of NCH, which are performed using a single-pulse shock tube (SPST). The SPST experiment is performed at pressure of 10 bar, temperature ranging from 1070 to 1560 K, reaction time of around 1.77 microsecond with fuel concentrations of 0.5 % diluted by Argon gas. The developed detailed kinetic mechanism exhibits reasonable prediction results of the pyrolysis product distributions together with literature ignition delay times across a wide range of temperature, pressure, and equivalence ratio conditions. Rate-of-production analysis is conducted to gain insight into the pyrolysis chemical kinetics of NCH. The present work should be valuable for the study of the combustion chemistry of nitro-alkane energetic fuels.

Experimental and numerical study of laminar burning velocity for Diisobutylene+ PRF/TRF mixtures

DIB (Diisobutylene, JC8H16) strongly correlates with real gasoline and significantly impacts the combustion behavior of alternative fuels designed as gasoline substitutes. However, accuracy concerns persist in laminar burning velocity data reported in literature. In this paper, the laminar burning velocities of DIB + air, DIB + PRF + air, and DIB + TRF + air mixtures were measured by the heat flux method at 1 atm. (PRF, Primary Reference Fuel; TRF, Toluene Reference Fuel) The equivalence ratio was controlled within 0.6–1.3, and the initial temperatures were set at 298K, 318K, and 338K. Additionally, by employing the mechanism proposed by Ren et al., the simulated values align with the experimental data, thus prompting the conduction of a reaction kinetic analysis. The analysis of chemical reaction kinetics reveals the reaction pathways of DIB, with a notable observation that an increase in temperature or a decrease in equivalence ratio can both lead to an elevation in the degree of unsaturation in the bonds of intermediate species. During laminar flame combustion, PRF and TRF compete with DIB for oxygen, with PRF appearing to have a stronger ability to capture oxygen. In addition, the laminar burning velocity temperature dependence coefficient α decreases first and then increases with the increase of the equivalence ratio, where the minimum α is obtained at equivalence ratio = 1.1. Additionally, the laminar burning velocity at higher initial temperatures is estimated by the extrapolation method and compared with the experimental data reported in literature.

Development of alternative for gypsum-based plaster using magnesium carbonates from carbon capture and utilization process

This study demonstrated the use of nesquehonite (MgCO3×3 H2O) in producing plasterboard. Nesquehonite (NQ) can be activated via thermal treatment under 50–175°C, after which the dehydrated nesquehonite can hydrate to form a plaster-like product, like gypsum-based plaster. Here, we developed different blends of NQ and hemihydrate (dehydrated gypsum) to produce plaster. In addition, the influence of trace elements (i.e., sulfate and ammonium) on the reaction kinetics, mechanical properties, microstructure, phase assemblage, and evolution of the developed plasters were investigated. The target was to achieve comparable manufacturing process and compressive strength with the conventional gypsum plaster process using NQ as a major precursor. Data revealed that the mixes containing 75 % NQ obtained from 2 different synthesis routes (i.e., wet carbonation or chemically-synthesis route) attained 6–8 MPa compressive strength after 28 days of curing, which was comparable to those observed in gypsum-based products. The chemically synthesized NQ achieved the stability of NQ in the plasterboard sample, while the use of wet-carbonated NQ led to the formation of dypingite. Furthermore, the water resistance of plasterboard mixes with 100 % NQ outperformed that of gypsum, without any decline in compressive strength after water exposure.

Effect of raw material fineness on the properties of inorganic foam materials from solid waste

Solid waste inorganic lightweight materials not only compensate for the flammability of organic materials but also have a lower carbon footprint. They are environmentally safe and cost-effective compared with cement-based foaming materials, and they have good development prospects. This study aimed to improve the chemical foaming reaction kinetics by reducing the particle size of aluminum powder and alkaline solid waste, thereby increasing the expansion degree of solid waste slurry, to further reduce the absolute dry density of inorganic lightweight materials for solid waste and optimize their performance. The influence of the particle size of raw material on the absolute dry density, water absorption, and compressive strength of lightweight materials was investigated. The influence of the particle size of raw material on the macroscopic pore structure of foamed materials was analyzed through binarization of cross-sectional images of specimens. Furthermore, the hydration products and microstructure of materials were characterized using XRD, FTIR, TG-DTG, and SEM to provide a theoretical basis for related research. The experimental results showed that the smaller the particle size of the raw material, the easier it was to carbonize and the lower the flowability of the corresponding cementitious material slurry. Reducing the particle size of raw materials and aluminum powder increased the degree of slurry expansion, thereby reducing the absolute dry density of foaming materials. In addition, reducing the particle size of raw materials and using carbide slag wastewater instead of tap water increased the degree of foaming reaction and hydration reaction, which helped C-(A)-S-H gel formation and promoted the development of sample strength. Finally, the absolute dry density of inorganic lightweight materials was reduced to 0.35 g/cm3 at the minimum, and the corresponding 28-day compressive strength was 0.28 MPa, which met the requirements of the JG/T 266–2011 “foam concrete” specification.

Regulating the evolution of interfacial species via B, N-codoped Pt sites for oxygen reduction electrocatalysis

The sluggish kinetics of the oxygen reduction reaction (ORR) poses significant limitations to the widespread application of the ORR in advanced energy systems. Here, we present a composite catalyst consisting of Pt nanoparticles immobilized on 3D B, N-doped graphene oxide (Pt/GO-BCN). Through X-ray absorption fine structure spectroscopy and synchrotron infrared spectroscopy analyses, we discovered that the codoping of B and N significantly regulates the electronic structure of graphene and enhances the interaction between Pt nanoparticles and the supports. The electronic state-optimized 3D support promotes the uniform distribution of Pt nanoparticles with small size, forming a low-resistance interfacial environment to accelerate the cleavage of the *OOH species during the reaction process. The ORR activity and selectivity of Pt/GO-BCN significantly surpassed those of commercial Pt/C catalysts, and excellent electrochemical performance under long-term operation was achieved. These results provide a new avenue for the design of advanced Pt-based catalysts.

Improving dairy manure hydrolysis and acidification through microbial community restructuring by adaptation to hyperthermophilic conditions

Dairy manure (DM) contributes significantly to greenhouse gas emissions and ecosystem degradation, yet its resistance to biodegradation hinders widespread bioprocessing applications. Lignocellulosic materials in DM pose a particular challenge because of their recalcitrance. Bioprocessing under hyperthermophilic (≥70 °C) conditions potentially offers an advantage over traditional fermentation temperatures due to enhanced activity of enzymes and the kinetics of enzymatic reactions. This can lead to a higher conversion rate and a greater extent of biomass hydrolysis and acidification. To test the validity of this hypothesis, the current study evaluated the efficacy of anaerobic hydrolysis and acidogenic fermentation of DM under mesophilic, thermophilic, and hyperthermophilic conditions. All inocula were adapted to corresponding temperatures but were derived from the same mesophilic source. Hyperthermophilic conditions resulted in superior DM hydrolysis efficiency (53%) compared to mesophilic (34%) and thermophilic (42%) conditions. The hyperthermophilic environment was particularly favorable to the decomposition of crude proteins and hemicellulose, which were reduced by 64% and 54%, respectively. Furthermore, hyperthermophilic fermentation also yielded the highest volatile fatty acid (VFA) production rate of 460 mg/L/day during the first four days, representing improvements of 50% and 90% over mesophilic and thermophilic conditions. In part, this was attributed to the enhanced production of branched-chain VFAs, including an increase of 6–10% in isobutyric acid and 12–13% in isovaleric acid. At hyperthermophilic conditions, however, there was no accumulation of VFAs during the days 5–8 of fermentation, which could be due to acetate conversion by the syntrophic acetate-oxidizing bacteria. A considerable gain in hydrolysis efficiency and VFA production rate were accompanied by a reduction in microbial diversity, which suggests that hyperthermophilic temperature is a favorable environment for the selection of organisms with enhanced DM hydrolysis and fermentation capabilities. A significantly increased relative abundance of xylanolytic Caldicoprobacter (23% of population) and proteolytic Thermovirga (9% of population) could be the major contributors to improved decomposition of hemicellulose and protein. As revealed by the techno-economic analysis, acidogenic fermentation of DM at 70 °C and a retention period of 4 days provides the greatest positive net present value, highest internal rate of return of 9.2%, and shortest investment payback period of 9 years. This study demonstrates that hyperthermophilic conditions enable superior deconstruction and bioconversion of lignocellulose-containing biomass into VFAs under reduced retention times, offering a promising approach for improving DM management and generating bioproducts.

Synthesis of Alpha Ferrous Oxalate Dihydrate from Ferrotitaniferous Mineral Sands via Hot Pressurized Aqueous Oxalic Acid: Kinetics and Characterization

Ferrous oxalate dihydrate is a versatile organic mineral with applications across fields. However, little is known about the feasibility of its synthesis directly from iron-bearing minerals using binary subcritical water (sCW) systems and its associated kinetics. In this study, the sCW+oxalic acid system at either 115 °C or 135 °C was investigated as a reaction medium for ferrous oxalate dihydrate (α-FeC2O4∙2H2O) synthesis, starting from ferrotitaniferous sands. The kinetics of the synthesis reaction were studied, and the physicochemical characterization of the as-synthetized ferrous oxalates was performed. Overall, the sCW synthesis was temperature-dependent, following second-order reaction kinetics according to the proposed precipitation pathway. A high reaction rate constant, significantly high yields (up to 89%), and reduced reaction times (2–8 h) were evident at 135 °C. The as-synthetized product corresponded to the monoclinic α-FeC2O4∙2H2O, showed relatively high specific surface areas (from 31.9 to 33.7 m2∙g−1), and exhibited band gap energies within the visible light range (~2.77 eV). These results suggest that α-FeC2O4∙2H2O can be synthesized using an organic dicarboxylic acid and iron-rich, widely available, low-cost mineral precursors. In addition, the as-prepared α-FeC2O4∙2H2O could be further optimized and tested for catalytic and visible light photocatalytic applications.

Accelerating Kinetics of Alkaline Hydrogen Oxidation Reaction on Ru through Engineering Oxophilicity

Accelerating Kinetics of Alkaline Hydrogen Oxidation Reaction on Ru through Engineering Oxophilicity

MnS doping regulating Co active sites on fibrous cobalt nitride as bifunctional oxygen electrocatalyst for high-performance Zn-air battery

Aiming to achieve high-efficiency bifunctional catalysts, doping engineering is applied to construct bifunctional catalysts for oxygen electrodes in Zn-air batteries to strengthen the catalytic kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, MnS doped cobalt nitride catalyst (MnS/CoNx) with divergent fiber morphology is prepared by low temperature nitriding for the self-assembling layered double hydroxides (LDH). The MnS/CoNx shows excellent electrical conductivity and improved catalytic activity on ORR and OER with low overpotential of 290 mV at 10 mA cm−2 and a good half-wave potential of 0.80 V in ORR compared with CoNx and MnO/CoNx. The contribution of the increased bifunctional catalytic performance is possible from the more active center Co3+ and Mn4+, and the elevated electron transport resulted from the opportune high conductive MnS doping. The MnS/CoNx catalyst-driven Zn-air battery achieves a higher power density of 228 mW cm−2 and the excellent long-term stability of 500 h at 20 mA cm−2 far surpassing the commercial Pt/C+RuO2 catalyst.

Performance of mesoporous ceria supported Ru catalysts for oxidative degradation of aqueous solution of plastic monomer bisphenol A in a fixed bed flow reactor: Structure-activity insights, optimization of reaction conditions, kinetics, catalyst stability, and characterization

One of the important defects is the oxygen vacancy on metal oxide surfaces, and the defects function as the active sites in different catalytic reactions. Herein, Ru/CeO2-rod and Ru/CeO2-cube catalysts were prepared via the ESI method, and CeO2-rod and CeO2-cube supports were synthesized by hydrothermal processes. The activity of these catalysts was tested in a high-pressure fixed-bed reactor, and the oxidative degradation of industrial organic raffinate containing the plastic chemical bisphenol A (BPA) was compared with their oxygen vacancy concentration estimated after calcination. The Ru/CeO2-rod catalyst showed higher catalytic activity with 90 % BPA conversion at 453 K, 30 bar, 0.5 % Ru metal content, 15 O2 to BPA molar ratio, and 2 g−1.h−1 BPA feed weight hourly space velocity (WHSV). In contrast, 80 % BPA degradation was achieved using the Ru/CeO2-cube catalyst under similar reaction conditions. The higher oxygen vacancy concentration and the higher interfacial surface area between metal and the support of the CeO2-rod supported Ru catalyst triggered the higher BPA degradation at low oxidation conditions. Besides, the atomic ratio, Ce3+/Ce4+, is lower in the Ru/CeO2-rod catalyst than that of the Ru/CeO2-cube catalyst, indicating the higher Ce4+ available in the catalyst, leading to the higher degradation of BPA. Moreover, the Ru/CeO2-rod catalyst possesses {111} planes that boost the generation of energetic Ru to improve the pursuit of the catalyst. The Weisz-Prater modulus and Thiele modulus values indicated that the surface reaction is the rate limitation step and there is no diffusion limitation. TEM, HRTEM, XPS, Raman, H2-TPR, XRD, CO chemisorption and BET surface area analyzers were used to characterize the catalysts.

Zirconium titanium phosphonates for enhanced lanthanide recovery from acidic wastes

Metal phosphonates show promise for recovery of valuable lanthanide (Ln) elements from acidic waste streams due to their selectivity, high capacity, fast kinetics and chemical stability. To optimise these properties, a balance is needed between free phosphonate groups available to bind Ln and P-O-metal linkages to provide stability. This work demonstrates how astute choice of metal precursors can be used to control the phosphonate structure and maximise both sorption and stability. Relative to single metal zirconium phosphonate, mixed metal zirconium titanium phosphonate sorbents had more free phosphonate groups and greater porosity, increasing Ln capacity by 30 % and the kinetic rate constant by 90 %. Acid stability was also improved upon Ti inclusion. Use of metal propoxide and tert-butoxide precursors were also compared, revealing different reactivities with Zr versus Ti. Specifically, the tert-butoxide precursor increased P-O-Zr linkages and acid stability with Zr, but increased formation of leachable P-O-Na2 groups in the presence of Ti that decreased acid stability. The optimised zirconium titanium phosphonate sorbent used metal propoxide precursors and a Zr:Ti molar ratio of 1:1 to achieve (1) selectivity for Ln over Co, Sr and Cs, (2) sorption capacity of approximately 70 mg Eu/g, (3) fast kinetics with > 99 % sorption in 10 min and (4) retention of 60 % sorption capacity after contact with 5 M nitric acid. The enhanced chemical stability, capacity and kinetics achieved via incorporating Ti drastically improves the practicality of these sorbents for Ln recovery from acidic leachates of magnets, phosphors and other wastes.