H2O2 Aqueous Solution Research Articles

Oxygen Vacancy-Rich TiO2 as an Efficient Non-noble Metal Catalyst toward Mild Oxidation of Methane Using Hydrogen Peroxide as the Oxidant

Direct functionalization of methane remains a key challenge, especially for using non-noble metal catalysts. We demonstrated that TiO2 nanorods with abundant oxygen vacancies enabled mild oxidation of methane by H2O2 into formaldehyde (HCHO) without light irradiation. The activity of TiO2 nanorods with the concentration gradient of oxygen vacancies (VO) increased with the VO concentration. In H2O2 aqueous solution under 30 bar of CH4 at 70 °C for 1 h, the TiO2 nanorods with the most abundant VO exhibited a total oxygenate yield of 40.80 μmol, among which the selectivity for HCHO was 64.1%. On the basis of the catalytic and spectroscopic data, we identified the reaction intermediates and accordingly mapped the reaction scheme. Specifically, H2O2 is activated on Ti atoms near VO to form surface peroxo intermediates, followed by the activation of CH4 to produce methoxy groups. The methoxy group can react either with water to form methanol or with hydroxyl radicals to form CH3OOH. Methanol is attacked by hydroxyl radicals and dehydrated to form •CH2OH that further reacts with hydroxyl radicals and is dehydrated to HCHO. CH3OOH directly undergoes dehydration to engender HCHO.

Catalytic activity of Mn(III) porphyrin complex supported onto cross linked polymers in the green oxidation of malathion with hydrogen peroxide in aqueous solution

Developing effective, affordable, and recoverable heterogeneous catalysts is one of the foremost challenges in modern chemistry. Mn(III) complexes of 5-(4-aminophenyl) −10, 15, and 20-triphenyl porphyrin 1 immobilized covalently on polymethyl methacrylate (PMMA) 2 and poly(methyl methacrylate –co- styrene) (PMMA/ST) 3 were synthesized, characterized, and applied for degradation of malathion with H2O2 in aqueous solution. Mn(III) porphyrin complex anchored on cross linked polymers 4 and 5 show high catalytic activity for malathion (pesticide) degradation in an aqueous solution with green oxidant H2O2. The catalytic efficacy of malathion degradation was highest with the Mn(III) porphyrin complex covalently anchored on (polymethyl methacrylate-co-styrene) 5. The optimum conditions, including the effect of pH, catalyst concentration, and H2O2 concentration on the degradation of malathion, were investigated. The reuse and stability of catalysts were examined, and the findings proposed that the Mn(III) porphyrin complex 5 has no noticeable changes in the removal efficiency up to five consecutive cycles. GC–MS analyses showed that the degraded compounds and intermediates formed from malathion degradation were non-toxic to E. coli bacteria. For the degradation of dissolved malathion pesticides in an aqueous solution, the use of Mn(III) porphyrin complex 5 in the presence of H2O2 has the potential to be advantageous.

Experimental and modelling approach to the design of chemical absorption columns with fast gas-liquid reaction: A case-study on flue-gas desulfurization with H2O2 oxidative solutions

In this work, we propose a methodology to approach the design of chemical absorption columns with fast gas-liquid reactions by an experimental and modelling study, which accounts for thermodynamic (solubility) data, mass-transfer phenomena, and the reaction kinetics contribution. As a reference case, the SO2 absorption in aqueous solution of H2O2 at different concentrations, which oxidizes SO2 to sulfuric acid, is considered. A lab-scale fed-batch bubble column is used to evaluate SO2 solubility dataset in absorbing solutions of distilled water containing different dosages of H2O2. A thermodynamic model is developed and validated in a Thermodynamic Flash block of ASPEN PLUS®, allowing to describe the experimental results with optimum agreement. For kinetic experiments, a lab-scale falling-film absorber is used to investigate both SO2 mass-transfer rates and the fundamental kinetic aspects of an absorption process with chemical reaction. The physical contribution to the mass-transfer rate is evaluated through a set of dedicated experiments, which allowed determining gas-side (kGa) and liquid-side (kLa) coefficients in the falling-film absorber. Subsequently, the Enhancement factor (EL) of the SO2 oxidative absorption is evaluated for the oxidizing reaction (SO2 + H2O2 → H2SO4) under the explored experimental conditions, using the equilibrium dataset and the mass transfer coefficients previously obtained. Finally, EL is correlated to the Hatta number (Ha) with the Danckwerts kinetic model as a pseudo-mth-nth-order non-reversible reaction type and the model kinetic parameters are calculated.

PEDOT:PSS/PEDOT Film Chemiresistive Sensors for Hydrogen Peroxide Vapor Detection under Ambient Conditions

Hydrogen peroxide (aqueous solution of H2O2) is one of the most used reagents i n medical sterilization, environmental disinfection, food storage, and other fields. However, hydrogen peroxide has the potential to cause serious harm to biological health and environmental safety. There are many methods (especially electrochemistry) for H2O2 detection in liquid phase systems, but a lack of methods for vapor detection. This is due to its colorless and tasteless nature, as well as the oxidative activity of the molecule and its coexistence with humidity. In this study, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), one of the most commercially successful and widely used conductive polymers, was employed to fabricate an all-organic chemiresistive sensor for simple, real-time, and on-site sensing of hydrogen peroxide vapor (HPV) at room temperature. In comparison with pristine PEDOT:PSS film, the PEDOT:PSS/PEDOT film was prepared by in situ electrochemical polymerization. Upon exposure to different concentrations of HPV, it was found that the hydrophobic and porous PEDOT layer could weaken the interference of humidity in HPV sensing, resulting in a more sensitive and accurate response. At 1.0 ppm HPV concentration, the resistance signal response was increased by nearly 89% compared with the pristine PEDOT:PSS film. This PEDOT-film-based chemiresistive sensor showcases the possibility for further development of nonenzymatic HPV monitoring technology.

Tunable molecular packing modes via H- or J-aggregates in the supramolecular helical nanostructures from an achiral C3 symmetric molecule.

The self-assembly of a C3-symmetric molecule benzene-1,3,5-tricarboxylate substituted with methyl cinnamate (BTECM) has been investigated by a reprecipitation method in H2O and cetyltrimethylammonium bromide (CTAB) aqueous solution, respectively. The nanostructures and characteristics of the assemblies were monitored by UV-Vis spectroscopy, fluorescence (FL) spectroscopy, circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that helical nanostructures were successfully assembled from the achiral C3 molecule BTECM. More importantly, the helices aggregated via different packing modes in H2O and CTAB aqueous solution. In H2O, the nanostructures underwent a process of particles, fibers and helices via H-type aggregate upon aging. In the case of CTAB aqueous solution (1.2 mM), the helices were translated from particles and the molecules were inclined to aggregate via the J-type mode. In addition, the aggregation process could be accelerated by raising the temperature proved by UV-Vis spectra. A molecular aggregation mechanism was proposed based on the experimental results.

Dissolution Assay of Bupropion/Naltrexone Hydrochloride Salts of Bilayer Composition Tablets Following the Development and Validation of a Novel HPLC Method

Compounded medicinal products containing bupropion hydrochloride (BUP·HCl) and naltrexone hydrochloride (NTX·HCl) are available as adjunct therapy for the management of weight in obese/overweight adults. The present work describes the development and validation of a novel RP-HPLC method for a simultaneous quantitation during the dissolution of both drugs from compounded bilayer composition tablets. The method involves a Nucleosil 100-3 C-18 column (4.6 × 150 mm) and a mobile phase of a 70%/30% v/v ACN/KH2PO4·H2O aqueous solution of a 5 mM concentration. The flow rate was set at 1.35 mL/min and the detection was conducted using UV spectrophotometry (λmax 214 nm). The method was validated according to the ICH guidelines and fulfilled the specifications for the specificity, linearity, accuracy, precision and stability for both the sample and standard solutions. Furthermore, the robustness of the method was evaluated by applying a fractional factorial experimental design and by utilizing both graphical and statistical approaches to identify the HPLC factors that should be strictly controlled during the analysis. The method proved to be suitable for the analysis of the dissolution samples and, consequently, the release of BUP·HCl and NTX·HCl from the formulations.

Core-Shell Structured Hemoglobin Nanoparticles as Artificial O2 Carriers.

This paper describes the synthesis and O2 binding properties of core-shell structured hemoglobin (Hb) nanoparticles (NPs), artificial O2 carriers of five types, as designed for use as red blood cell (RBC) substitutes. Human adult Hbs were polymerized using α-succinimidyl-ω-maleimide and dithiothreitol in spheroidal shapes to create parent particles. Subsequent covalent wrapping of the sphere with human serum albumin (HSA) yielded 100 nm-diameter Hb nanoparticles (HbNPs). The HbNP showed higher O2 affinity than that of RBC, but NPs prepared under a N2 atmosphere exhibited low O2 affinity. Entirely synthetic particles comprising recombinant human adult Hb and recombinant HSA were also fabricated. Using a recombinant Hb (rHb) variant in which Leu-β28 of the heme pocket had been replaced with Phe, we found somewhat low O2 affinity of rHb(βL28F)NP. Particles made of stroma-free Hb (SFHb) containing natural antioxidant enzyme catalase (SFHbNP) formed a very stable O2 complex, even in aqueous H2O2 solution. The SFHbNP showed good blood compatibility and did not affect the blood cell component functionality. The circulation half-life of SFHbNP in rats was considerably longer than that of naked Hb. All results indicate these Hb-based NPs as useful alternative materials for RBC and as a useful O2 therapeutic reagent in diverse medical scenarios.

The green synthesis of oligo(azomethine)s based on p-anisidine and o-anisidine: reaction conditions, electrochemical and thermal properties

Schiff bases and their conjugated oligo(azomethine)s have been synthesized via condensation and oxidative polycondensation of o-anisidine (OA) with 2-hydroxy-1-naphthaldehyde (2-HNA) and p-anisidine (PA) with 4-hydroxy benzaldehyde (4-HBA), respectively. The oxidative polycondensation reaction conditions of 1-[(2-methoxyphenylimino)methyl]naphthalen-2-ol (1,2-MPIMN) and 4-[(4-methoxyphenylimino)methyl]phenol (4,4-MPIMP) were studied by oxidants such as air and aqueous solutions of H2O2 and NaOCl in different concentrations in an aqueous alkaline medium between 50 °C and 90 °C at different reaction times. The structures of polymers were confirmed by FT-IR, UV-Vis and 1H-13C-NMR measurements. The molecular weights and surface morphologies of oligomers were determined by size exclusion chromatography (SEC) and scanning electron microscopy (SEM), respectively. Electrochemical and thermal features of compounds were studied using UV-Vis spectroscopies, cycling voltammetry (CV), and TG-DTA. The mass losses values ​​of the 1,2-MPIMN, oligo(1,2-MPIMN), 4,4-MPIMP, and oligo(4,4-MPIMP) were calculated from the thermogravimetric curves as 98.00%, 53.52%, 69.00%, and 58.70%, respectively, at 1000 °C. The HOMO, LUMO levels, electrochemical (E’ g ), and optical band gap energies (Eg ) values of the compounds were calculated from CV and UV-Vis data. The E’ g values of 1,2-MPIMN, oligo(1,2-MPIMN), 4,4-MPIMP, and oligo(4,4-MPIMP) were found to be 2.64, 1.54, 2.31, and 2.16 eV, respectively. The electrical properties of monomers and oligomers were determined at room temperature.

A New Model Algorithm for Estimating the Inhalation Exposure Resulting from the Spraying of (Semi)-Volatile Binary Liquid Mixtures (SprayEva).

The spraying of liquid multicomponent mixtures is common in many professional and industrial settings. Typical examples are cleaning agents, additives, coatings, and biocidal products. In all of these examples, hazardous substances can be released in the form of aerosols or vapours. For occupational and consumer risk assessment in regulatory contexts, it is therefore important to know the exposure which results from the amount of chemicals in the surrounding air. In this research, a mechanistic mass balance model has been developed that covers the spraying of (semi)-volatile substances, taking into account combined exposure to spray mist, evaporation from droplets, and evaporation from surfaces as well as the nonideal behaviour of components in liquids and backpressure effects. For wall-spraying scenarios, an impaction module has been developed that quantifies the amount of overspray and the amount of material that lands on the wall. Mechanistically, the model is based on the assumption that continuous spraying can be approximated by a number of sequentially released spray pulses, each characterized by a certain droplet size, where the total aerosol exposure is obtained by summation over all release pulses. The corresponding system of differential equations is solved numerically using an extended Euler algorithm that is based on a discretisation of time and space. Since workers typically apply the product continuously, the treated area and the corresponding evaporating surface area grows over time. Time-dependent concentration gradients within the sprayed liquid films that may result from different volatilities of the components are therefore addressed by the proposed model. A worked example is presented to illustrate the calculated exposure for a scenario where aqueous solutions of H2O2 are sprayed onto surfaces as a biocidal product. The results reveal that exposure to H2O2 aerosol reaches relevant concentrations only during the spraying phase. Evaporation from sprayed surfaces takes place over much longer time periods, where backpressure effects caused by large emission sources can influence the shape of the concentration time curves significantly. The influence of the activity coefficients is not so pronounced. To test the plausibility of the developed model algorithm, a comparison of model estimates of SprayExpo, SprayEva, and ConsExpo with measured data is performed. Although the comparison is based on a limited number (N = 19) of measurement data, the results are nevertheless regarded as supportive and acceptable for the plausibility and predictive power of SprayEva.

Large‐Scale Self‐Assembly of MOFs Colloidosomes for Bubble‐Propelled Micromotors and Stirring‐Free Environmental Remediation

AbstractThe design of MOF‐based micromotors (MOFtors) is still challenging and with limited approaches, especially for the MOF nanoparticles (NPs). Herein, we report a universal and straightforward strategy to efficiently self‐assembly MOF NPs into robust MOFtors for enhanced organic‐ or heavy‐metal‐ion‐contaminants remediation without mechanical stirring. Based on the transient Pickering emulsion method, Fe3O4@NH2‐UiO‐66 (Fe‐UiO) NPs are rapidly self‐assembled into Fe3O4@NH2‐UiO‐66 colloidosomes (Fe‐UiOSomes) on a large scale, and the formation mechanism is systematically studied. The Fe‐UiOSomes‐Pt micromotors through chemical reduction (Micromotor‐C) presented a higher motility of 450±180 μm s−1 in a 5 wt% H2O2 aqueous solution. Finally, the bubble‐propelled Micromotor‐C was employed to efficiently remove dyes and heavy metal ions (94 % for MO and 91 % for CrVI).

Conformation, hydration, and ligand exchange process of ruthenium nitrosyl complexes in aqueous solution: Free-energy calculations by a combination of molecular-orbital theories and different solvent models.

Distribution of solvent molecules near transition-metal complex is key information to comprehend the functionality, reactivity, and so forth. However, polarizable continuum solvent models still are the standard and conventional partner of molecular-orbital (MO) calculations in the solution system including transition-metal complex. In this study, we investigate the conformation, hydration, and ligand substitution reaction between NO2 - and H2 O in aqueous solution for [Ru(NO)(OH)(NO2 )4 ]2- (A), [Ru(NO)(OH)(NO2 )3 (ONO)]2- (B), and [Ru(NO)(OH)(NO2 )3 (H2 O)]- (C) using a combination method of MO theories and a state-of-the-art molecular solvation technique (NI-MC-MOZ-SCF). A dominant species is found in the complex B conformers and, as expected, different between the solvent models, which reveals that molecular solvation beyond continuum media treatment are required for a reliable description of solvation near transition-metal complex. In the stability constant evaluation of ligand substitution reaction, an assumption that considers the direct association between the dissociated NO2 - and complex C is useful to obtain a reliable stability constant.

Investigation of chemical degradation and water states in the graft‐type polymer electrolyte membranes

AbstractChemical degradation in the presence of H2O2 aqueous solution and water states of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes (ETFE‐PEMs) with grafting degree (GD) of 8.8%–21.1% are investigated using Fourier‐transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). The ETFE‐PEMs show the complete detachment at the α‐hydrogen atoms of the whole graft PSSA chains from the ETFE backbones, while their precursor polystyrene‐grafted ETFE films do not. This chemical degradation exhibits independently with GDs and takes place even at very low GD (<10%). Water molecules of the membranes dried at 40°C are not completely de‐absorbed. The remains are partial non‐bonded water molecules, which are assumed to locate within the lamellar amorphous domains (constrained water molecules) of the crystalline phases. These constrained water molecules exist independently with the PSSA groups and do not detach together with them during the degradation. Note that the water molecules remained at 40°C show the additional contribution of 18%–19% to the total water uptake but do not contribute clearly to the conductance.

Coherent Raman comb generation in H2O2aqueous solutions by crossing-pump stimulated Raman scattering.

The cascaded stimulated Raman scattering (SRS) of 30% H2O2 aqueous solutions was investigated using a pulsed Nd: YAG laser with a wavelength of 532 nm. The transfer of excess electrons between H2O2 and H2O molecules enhanced the SRS. Together, the decomposition of H2O2 and the intense SRS Stokes led to the generation of the crossing-pump effect of H2O2 aqueous solutions and the appearance of a new peak at 4229 cm-1 that is excited by Stokes as the pump source. Crossing-pump not only reduced the threshold but also generated the broadband-coherent Raman comb, defined as a coherent radiation wavelength ranging from 434 to 831 nm (i.e., a Raman shift ranging from -4225 to 6756 cm-1). The anti-Stokes SRS was attributed to the four-wave mixing (FWM) process.

A Fluorescent Alcohol Biosensor Using a Simple microPAD Based Detection Scheme

A paper-based microfluidic detection device for the detection of ethanol is demonstrated in this work. The method is based on a fluorophore consisting of short-chain conjugated molecular unit susceptible to the protonation of its terminal pyridine groups, along with a carboxyl-functionalized sidechain that acts as a binder and renders it water-soluble. The resulting fluorescent paper device yields large fluorescence changes when exposed to reactions that yield H2O2 in aqueous solutions. Using an enzyme-catalyzed rection that produces H2O2 from ethanol, we developed a two-zone, cut-out paper device containing a reaction zone in which the ethanol-containing analyte is placed, and an adjacent sensor zone where we observe a fluorescence color shift proportional to the ethanol concentration. The limit of detection of the fluidic ethanol biosensor was 0.05 v/v% and the dynamic range was 0.05–2 v/v%. This method was employed to detect the alcohol concentration of consumer vodkas using only a paper sensor and a smartphone camera.

Integrated electron beam irradiation treatment with hydrogen peroxide aqueous solution to inactivate Salmonella on grape tomatoes

AbstractThis study investigated the efficacy of integrated electron beam (e‐beam) irradiation and hydrogen peroxide (H2O2) aqueous solution treatments to inactivate mixed strains of Salmonella inoculated in grape tomatoes. Whole grape tomatoes were inoculated with a mixed bacterial cocktail composed of five strains of Salmonella enterica corresponding to serotypes Rissen (SAL1449), Montevideo (SAL4599), Saintpaul (476398), and Typhimurium (ATCC 13311 and ATCC 700720), dried in a biological safety cabinet for 2 h at room temperature and then stored at 4°C for 24 h to facilitate bacterial attachment before treatment. Tomatoes in H2O2 (60 mg/L) aqueous solution were irradiated at 0.45, 0.60, 0.75, 1.0, and 1.25 kGy dose. The combined treatment of 1.0 kGy radiation dose and 60 mg/L H2O2 achieved 4‐log reductions in Salmonella. The D10−average value of Salmonella in the present study was 0.25 ± 0.01 kGy. Regarding the effect of the treatment on tomato quality, the combined application of e‐beam up to 1.25 kGy and H2O2 (60 mg/L) did not affect (p > .05) the color and texture of grape tomatoes compared to non‐irradiated samples. Furthermore, the combined treatments of e‐beam and H2O2 aqueous solution reduced the dose uniformity ratio (DUR) by 7%, a relevant finding regarding commercial applications of electron beam accelerators. Exposure of the tomatoes to e‐beam and water wash with added H2O2 is a promising decontamination system for use in tomatoes and other produce processing. Further studies on the optimization of this integrated treatment are needed.Practical ApplicationsElectron beam irradiation of tomatoes immersed in hydrogen peroxide (H2O2) solution reduces the dose required to eliminate pathogens in the fresh produce. The integrated treatment ensures minimal changes to produce quality and increased treatment efficiency in terms of dose uniformity.

Solar Light-Assisted Oxidative Degradation of Ciprofloxacin in Aqueous Solution by Iron(III) Chelated Cross-Linked Chitosan Immobilized on a Glass Plate

The massive worldwide use of antibiotics leads to water pollution and increasing microbial resistance. Hence, the removal of antibiotic residues is a key issue in water remediation. Here, we report the solar light-assisted oxidative degradation of ciprofloxacin (CPF), using H2O2 in aqueous solution, catalyzed by iron(III) chelated cross-linked chitosan (FeIII-CS-GLA) immobilized on a glass plate. The FeIII-CS-GLA catalyst was characterized by FTIR and 57Fe-Mössbauer spectroscopies as well as X-ray diffraction, revealing key structural motifs and a high-spin ferric character of the metal. Catalytic degradation of CPF was investigated as a function of solar light irradiation time, solution pH, concentration of H2O2 and CPF, as well as cross-linker dosage and iron(III) content in FeIII-CS-GLA. The system was found to serve as an efficient catalyst with maximum CPF degradation at pH 3. The specific ·OH scavenger mannitol significantly reduces the degradation rate, indicating that hydroxyl radicals play a key role. The mechanism of catalytic CPF degradation was evaluated in terms of pseudo-first-order and Langmuir-Hinshelwood kinetic models; adsorption of CPF onto the FeIII-CS-GLA surface was evidenced by field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. FeIII-CS-GLA can be reused multiple times with only minor loss of catalytic efficiency. Antimicrobial activity tests performed against both Gram-negative (Escherichia coli DH5α, Salmonella typhi AF4500) and Gram-positive bacteria (Bacillus subtilis RBW) before and after treatment confirmed complete degradation of CPF. These results establish the immobilized FeIII-CS-GLA as a rugged catalyst system for efficient photo-Fenton type degradation of antibiotics in aqueous solutions.

The Use of Plasmonic Spectroscopy for Detecting Ultra-Low Concentrations of Substances

This paper presents the results of research into the excitation of a surface electromagnetic wave (SEW) in Au/AgI and Au/Ag films contacting aqueous solutions of hydrogen peroxide (H2O2) and sodium chloride (NaCl). The dependences of the SEW excitation angle in the Kretschmann configuration on the interaction time of the solution with the metal film have been obtained. The effect of an aqueous H2O2 solution on the AgI and Ag film under prolonged exposure has been demonstrated. It has been shown that the dynamics of the excitation angle can be used to estimate the concentration of solutions with low and ultra-low concentrations. As an example, the results of using the technique for the analysis of aqueous solutions of NaCl are presented.

Recovery of platinum from diesel catalysts by combined use of H2O2/HCl leaching and adsorption

Spent automotive catalysts are industrial non-hazardous wastes of high added values because of the presence of platinum group metals, whose recovery is gaining increasing attention in European countries. This paper proposes a hydrometallurgical process to recover platinum from diesel catalysts, based on a first leaching step with aqueous solutions of H2O2 (up to 0.2 M) and mild HCl concentrations (0.4 M), followed by a refining step in which platinum is deposited over a granular activated carbon. Tests were carried out at different H2O2 content, temperatures, and sizes of granulated catalyst. The use of H2O2 and low HCl content allows higher sustainability than conventional hydrometallurgical processes by reducing safety risks associated with the use of concentrated HCl and the emissions of NOx deriving from the use of nitrogen species in conventional leaching. Besides, the use of an adsorbent avoids the utilization of cyanides or other toxic organic solvents for the refining of the leaching solution. Experiments revealed that the low HCl concentration results in longer leaching times; however, process conditions can be tuned to completely recover platinum with negligible extraction of other metals on the catalyst, minimizing on the subsequent adsorption process. Optimal conditions appear as leaching at 20 °C with a 0.13 M H2O2 0.4 M HCl solution followed by an adsorption step at 20 °C using an activated carbon with high BET surface area and high content of reducing surface groups. These findings suggest that the proposed recovery process can be a suitable candidate for future technology implementations.

Layered mesoporous SnO2 for effective ethanol detection at reduced working temperature

Tin oxide is widely studied for ethanol sensing because of its high sensitivity and environmental benignity; yet its operating temperatures generally exceed 200 °C to achieve an acceptable overall sensing performance. In this study, we report a layered mesoporous aggregate of SnO2 nanocrystals 3–5 nm in size, which is synthesized by oxidizing metallic tin particles in a mixed aqueous solution of HNO3 and H2O2 at 80 °C. The aggregate calcinated at 300 °C possesses a high specific surface area of 135 m2 g−1, and 0.182 cm3 g−1 mesopores ca. 2.5 nm in size. At an operating temperature of 180 °C, the SnO2 aggregate exhibits a response of 110 towards 100 ppm ethanol in air. At an even lower working temperature of 140 °C, an ideal overall sensing performance is achieved: a response of 37, a response/recovery time of 26/21 s, together with high selectivity and stability. The layered mesoporous architecture with a high specific surface area contributes to the high response at low operating temperatures. Besides, with increasing operating temperatures from below to beyond 150 °C, it takes much a longer time to achieve a total recovery in resistance. The ethanol sensing mechanism is thus believed to change accordingly from the direct adsorption one to the oxygen ionosorption model.

On-site H2O2 production with amphiphilic g-C3N4 as photocatalyst in a combined photocatalysis–extraction–separation process

Hydrogen peroxide (H2O2) can be photocatalytically generated by oxygen in water with fatty alcohols as a sacrificial agent; however, it is expensive to separate because of the miscibility of fatty alcohols and water. In this work, H2O2 is directly generated photocatalytically using amphiphilic graphitic carbon nitride (g-C3N4) and oxygen in pure anhydrous oily benzyl alcohol (BA) alone; it is simply extracted by water and separated using a hydrophobic/lipophilic mesh to obtain a high-concentration H2O2 aqueous solution. The results show that the H2O2 concentration in BA after 4 h of photoreaction is 9.45 mM and that of the final solution product can be as high as 70.93 mM in water. Water does not enhance the photoreaction; instead, unexpectedly, it weakens it. However, it is possible to completely extract the H2O2 from the reacted BA. In this study, the H2O2 solution is rapidly separated from the BA with a separation efficiency of 99.97% using a hydrophobic mesh. The photocatalyst g-C3N4 is present at the water/BA interface owing to its amphiphilicity, and it can be caught by the mesh during separation and reused after backwashing. The combined photoreaction, extraction, and separation processes provide a simple, environment-friendly, and rapid H2O2 photogeneration process for the on-site production of a usable H2O2 solution.