HNO3 Aqueous Solution Research Articles

Removal of methylene blue from aqueous solutions by adsorption onto Carpobrotus edulis biomass

The aim of this work is to investigate the influence of an alkaline pretreatment of the Mediterranean plant Carpobrotus edulis on the adsorption capacity toward the dye methylene blue and to estimate the content of soluble organic matter that can be released into the aqueous solution by this biomaterial. The biomaterial used was characterized by SEM-EDX, SS, FT-IR, pHZ, COD and BOD5. Removal of methylene blue (MB) dye by this biomaterial was carried out and the effects of physicochemical factors such as initial pollutant concentration, adsorbent dose, contact time, pH and temperature were investigated. After adsorbent treatment, the soluble organic matter was reduced by 97%, 96%, and 96% for biological oxygen demand, chemical oxygen demand, and organic matter, respectively. Kinetics and equilibrium studies of MB adsorption on the bioadsorbents were fitted with a pseudo-second order kinetic model and a Langmuir model, respectively. The maximum adsorption amount of the modified C. edulis plant was 153.9 mg/g at 298°K. The thermodynamic parameters show that the adsorption process was possible and spontaneous in nature. The adsorption mechanism of MB on the surface of biomaterials was attributed to the electrostatic interaction and H-bonding. The prepared biomaterial (0.016 U$ per gram) was easily regenerated with aqueous HNO3 solution, with a slight decrease in adsorption capacity up to five cycles. The results of Taguchi experimental design and analysis of variance showed that contact time, adsorbent mass and initial concentration are the most important factors affecting the removal efficiency with a contribution of 43.91%, 32.68%, and 22.95%, respectively. The maximum removal capacity of MB dye in optimal operating conditions was 99.39%, which was obtained at the optimum conditions of m = 1 g, pH 4, T = 35 °C, Ci = 1000 mg/L, tc = 5 min. These results confirm previous results obtained with the batch system and show that this absorbent is also promising for the removal of cationic dyes from wastewater.

Comparative analysis of rheological characteristics for chemically treated and untreated COSL with varying minerals matter at low temperature

Indian coal having ash content of 38.5 % by wt. with particle size below 106 µm underwent treatment with an aqueous solution of HF and HNO3 at ambient conditions, maintaining a coal-to-solvent ratio of 3:20. Following this treatment, the ash content decreased significantly to 0.9 % by weight. However, the calorific value of the coal decreased from 4865 Kcal/kg to 4766 Kcal/kg because of chemical attack on the carbonaceous matrix. Additionally, sulfur content decreased as iron was oxidized when it reacted with HNO3 to form sulfate compounds. To examine the impact of mineral matter available in coal, a slurry was prepared using both untreated and chemically washed coal, mixed with diesel oil (with calorific value of 44,600 kcal/kg). The research was conducted using a rotary-type Anton Parr RheolabQC at three different solid concentration levels (20 %, 30 %, and 40 %) of coal in oil at a temperature of 293 K. The results revealed that mineral content had a fundamental determinant on the viscosity of COSL. The ultra-clean COSL exhibited the highest viscosity across all concentrations, while viscosity decreased as the percentage of treated coal decreased. Furthermore, viscosity reduced with enhanced in shear rate, and all slurries exhibited shear-thinning behavior. Scanning Electron Microscopy (SEM) analysis indicated the presence of nonporous ash materials in untreated coal, which contributed to its lower viscosity.

Tailored Exfoliation of Polymeric Carbon Nitride for Photocatalytic H2O2 Production and CH4 Valorization Mediated by O2 Activation.

The exfoliation of bulk C3N4 (BCN) into ultrathin layered structure is an effective strategy to boost photocatalytic efficiency by exposing interior active sites and accelerating charge separation and transportation. Herein, we report a novel nitrate anion intercalation-decomposition (NID) strategy that is effective in peeling off BCN into few-layer C3N4 (fl-CN) with tailored thickness down to bi-layer. This strategy only involves hydrothermal treatment of BCN in diluted HNO3 aqueous solution, followed by pyrolysis at various temperatures. The decomposition of the nitrate anions not only exfoliates BCN and changes the band structure, but also incorporates oxygen species onto fl-CN, which is conducive to O2 adsorption and hence relevant chemical processes. In photocatalytic O2 reduction under visible light irradiation, the H2O2 production rate over the optimal fl-CN-530 catalyst is 952 μmol g-1 h-1, which is 8.8 times that over BCN. More importantly, under full arc irradiation and in the absence of hole scavenger, CH4 can be photocatalytically oxidized by on-site formed H2O2 and active oxygen species to generate value-added C1 oxygenates with high selectivity of 99.2 % and record-high production rate of 1893 μmol g-1 h-1 among the metal-free C3N4-based photocatalysts.

Tailored Exfoliation of Polymeric Carbon Nitride for Photocatalytic H2O2 Production and CH4 Valorization Mediated by O2 Activation

AbstractThe exfoliation of bulk C3N4 (BCN) into ultrathin layered structure is an effective strategy to boost photocatalytic efficiency by exposing interior active sites and accelerating charge separation and transportation. Herein, we report a novel nitrate anion intercalation‐decomposition (NID) strategy that is effective in peeling off BCN into few‐layer C3N4 (fl‐CN) with tailored thickness down to bi‐layer. This strategy only involves hydrothermal treatment of BCN in diluted HNO3 aqueous solution, followed by pyrolysis at various temperatures. The decomposition of the nitrate anions not only exfoliates BCN and changes the band structure, but also incorporates oxygen species onto fl‐CN, which is conducive to O2 adsorption and hence relevant chemical processes. In photocatalytic O2 reduction under visible light irradiation, the H2O2 production rate over the optimal fl‐CN‐530 catalyst is 952 μmol g−1 h−1, which is 8.8 times that over BCN. More importantly, under full arc irradiation and in the absence of hole scavenger, CH4 can be photocatalytically oxidized by on‐site formed H2O2 and active oxygen species to generate value‐added C1 oxygenates with high selectivity of 99.2 % and record‐high production rate of 1893 μmol g−1 h−1 among the metal‐free C3N4‐based photocatalysts.

Development of eco-friendly pretreatment processes for high-purity silicon recovery from end-of-life photovoltaic modules.

This study examines the efficacy of photovoltaic (PV) recycling processes and technologies for the recovery of high-purity silicon powder from waste solar modules. In order to facilitate the simplification of complex processes, such as the conventional nitric acid dissolution, solvent and ultrasonic irradiation, and solvent dissolution, a variety of mechanical separation processes have been established. These processes are designed to enhance the efficiency and effectiveness of the aforementioned processes. And a novel method for separating EVA from recycled Si powder was devised, which studied the WGS process using aqueous solutions of H2O, HNO3, and NaCl with different specific gravities. The WGS process using NaCl solution demonstrated superior performance, removing over 94% of the EVA, requiring less energy input and producing 73% less CO2 emissions compared to the thermal process. These technologies facilitate the transition towards a circular economy and bolster the implementation of carbon-neutral initiatives.

Strong acid-mediated Ca2+ extraction–CO2 mineralization process for CO2 absorption and nano-sized CaCO3 production from cement kiln dust: Simultaneous treatment of CO2 and alkaline wastewater

Increasing yearly stockpiles of cement kiln dust (CKD) and the associated high landfilling cost require innovative solutions to utilize CKD. This study proposes a strong acid-mediated extraction–mineralization process that utilizes CO2. The process comprises the extraction of Ca2+ from CKD using strong acids, mineralization of CO2 using extracted Ca2+ and alkaline wastewater, and production of Ca carbonate. High Ca2+ leaching efficiency, high Ca2+ extraction efficiency, and high-purity nano-sized CaCO3 production from CKD were achieved under normal operating conditions in an in-situ strong acid solution. The process feasibility was primarily tested via an individual extraction process using aqueous HCl and HNO3 solutions from typical CKD and mineral carbonation experiments using Ca(OH)2 and alkaline wastewater obtained from the extraction process. The process had a Ca2+ leaching efficiency of 94.73%, Ca2+ extraction efficiency of 93.54%, and CaCO3 yield of 1.45 ton/ton CKD in the aqueous HCl solution. Polymorphism and crystal structure analyses showed that CaCO3 obtained after CO2 mineralization was mainly present as calcite. Alkaline wastewater acted as a pH buffer, enhanced the reactivity with CO2, accelerated the conversion of CO2(g) to CO32-(aq), and acted as an accelerator that promoted the nucleation growth of CaCO3 by OH- ions during the mineralization process. The effect of the nucleation and growth of CaCO3 on the particle and crystallite size is highly dependent on the system pH. These results can be applied to CO2 utilization processes by industrial by-products.

Acid-modulated synthesis of ultra-thin Ti-MWW zeolite nanosheets for the efficient epoxidation of cycloalkenes with tert-butyl hydroperoxide

The Ti-MWW zeolites with a layered morphology, synthesized by a conventional method, usually show low catalytic activities in the epoxidation of bulky alkenes due to the serious steric constraint imposed by the zeolite micropores and the adverse effects from some extra-framework octahedral Ti species. In the present work, the Ti-MWW zeolite was prepared by the reaction of an ultra-thin layered borosilicate MWW-type zeolite (D-ERB-1) with tetrabutyl orthotitanate (TBOT) in a HNO3 aqueous solution, wherein D-ERB-1 was hydrothermally synthesized by introducing an organosilane into the synthetic gel. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that the currently synthesized Ti-MWW zeolite without extra-framework octahedral Ti species has thinner nanosheets that are very helpful to the epoxidation of cycloalkenes with tert-butyl hydroperoxide (TBHP), and is more active than the conventional Ti-MWW and other titanosilicate zeolites. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by washing with acetonitrile (MeCN). Therefore, the present work provides some guidance in the development of an efficient titanosilicate catalyst for the epoxidation of bulky alkenes.

Selective capture of uranium and zirconium from strong HNO3 solution by ethenylphosphonic acid copolymerized polymer

The nuclear fuel rod contains mainly uranium (U) as the fuel and zirconium (Zr) as the cladding material. Improper disposition of the dissolved solution of the exhausted fuel rod releases radioactive acidic aqueous solution, which is a waste of U and Zr resources and also poses a great threat to the environment and living beings. The present work aims to selectively capture U and Zr from a 4 mol/L HNO3 aqueous solution in the presence of competing ions including La, Zn, Cd, Gd, Ce, Sr, Mn, Cu and Ba. Trimethylolpropane trimethacrylate (TMPTMA) copolymerized with ethenylphosphonic acid (EPA). TMPTMA improved the mesoporous character and adsorption ability of the adsorbent towards U and Zr. The synthesized polymer adsorbent was characterized by SEM, EDS, FT-IR, TGA, XRD, BET, XPS, and NMR to study the adsorption. The results indicated that the EPA-POP-2 adsorbent showed considerable adsorption capacity towards U(VI) (374.1 mg g−1) and Zr(IV) (217.4 mg g−1) in a strong HNO3 medium. Langmuir isotherm model fitted well to the experimental data, indicating that the monolayer adsorption process was dominating. The fitted pseudo-second-order (PSO) model represents that the adsorption mechanism is chemisorption. XPS, FT-IR, and DFT calculation results revealed that this adsorption capacity towards U and Zr was because of the P = O ligands present in the adsorbent. Van’t Hoff graph for U and Zr were also drawn to calculate the enthalpy, entropy, and Gibb’s free energy of the reaction. The reusability test showed that the adsorption capacity of synthesized adsorbent was high enough towards the U and Zr even after five consecutive cycles of adsorption and desorption.

Characterization of functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) are functionalized to determine structural and chemical changes occurred due to oxidation at room temperature in presence of an aqueous solution of concentrated HNO3. The raw and processed (functionalized) MWCNTs were investigated with FTIR and FESEM spectroscopy methods. The surface morphology was examined by FESEM and presence of carboxylic group were identified with Fourier Transform Infrared Spectroscopy (FTIR). The multi walled carbon nanotube of 8 nm, 10–30 nm & 50 nm were taken for experimentation. The FTIR spectra revealed that the broad peak @3450 cm-1 corresponds to O–H bond and peak at @ 1630 cm-1 corresponds to C = O bond. The intensity of both raw and functionalized MWCNTs peak signifies presence of COOH group. Likewise, FESEM images shows, agglomeration of MWCNTs due to Van der Waals forces in raw MWCNTs but after functionalization, unbundled CNTs with reduction in length due to breakage of C = C bond and presence of carboxyl group at end of CNTs.

Ti-MWW synthesis via acid-modulated isomorphous substitution of ERB-1 for efficient ethylene oxidative hydration to ethylene glycol

Although the oxidative hydration of ethylene with hydrogen peroxide (H2O2) to ethylene glycol (EG) over Ti-MWW zeolites take advantages of step-saving and facile operation, both H2O2 utilization efficiency and EG yield are relatively low, because some extra-framework octahedral Ti species are usually formed in the Ti-MWW zeolites synthesized by prevailing methods, which are detrimental to selective oxidation. In the present work, an acid-modulated isomorphous substitution method, i.e., layered borosilicate MWW-type zeolite (ERB-1) treated with HNO3 aqueous solution containing tetrabutyl orthotitanate (TBOT), is developed to synthesize a Ti-MWW zeolite without extra-framework octahedral Ti species under the optimized synthesis conditions. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that in the zeolite prepared by the currently developed synthesis method there are more open Ti(OSi)3OH sites formed, resulting in the stronger Lewis acidity that is very helpful to EG production from the oxidative hydration of ethylene with H2O2, compared to the one synthesized by the prevailing method. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by calcination at high temperatures. Therefore, it is anticipated that the currently developed Ti-MWW might be industrially applicable in the one-pot synthesis of EG from ethylene with H2O2.

MODIFICATION OF THE SURFACE OF COPPER ALLOYS WITH ALUMINUM IN THE CONDITIONS OF SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

The influence of the technological parameters of the SHS process (temperature, holding time and alloying of B, Cr, Ti) on the corrosion resistance of brass with a surface alite layer, which effectively resists β-radiation, was studied. The research was carried out in 30% aqueous solutions of HNO3, HCl, H2SO4. Aluminized coatings doped with silicon, which are obtained under optimal parameters, have 1.7-2.1 times higher corrosion resistance than doped B and Ti. Alloyed coatings have phases CuSi, CuAl, CuAl2, CuTi, Ti2Cu3, CuCr, Cu3Al, Cu2Al, Al3Si, and α-phase doped with Cr, Al, Si, B, Ti. When tested in a 30% aqueous solution of nitric acid, the coating doped with titanium and silicon shows a weight loss of 32 and 37 g/m2, respectively.

In-depth knowledge of the low-temperature hydrothermal synthesis of nanocrystalline hydroxyapatite from waste green mussel shell (Perna Viridis)

ABSTRACT This study presents the use of a low-temperature hydrothermal method for extracting calcium sources from green mussel shell (P. Viridis) wastes and converting them into synthetic nanosized hydroxyapatite (HA). In this study, raw mussel shells were washed, pulverised, and sieved to start producing a fine calcium carbonate-rich powder. XRD quantitative analysis confirmed that the powder contains 97.6 wt. % aragonite. This powder was then calcined for 5 h at 900 °C to remove water, salt, and mud, yielding a calcium-rich feedstock with major minerals of calcite (68.7 wt.%), portlandite (24.7 wt.%), and minor aragonite (6.5 wt.%). The calcined powders were dissolved in aqueous stock solutions of HNO3 and NH4OH before hydrothermally reacting with phosphoric acid [(NH4)2HPO4], yielding pure, nanoscale (16-18 nm) carbonated HA crystals, according to XRD, FT-IR, and SEM analyses. The use of a low-temperature hydrothermal method for a feedstock powder produced by the calcination of low-cost mussel shell wastes would be a valuable processing approach for the industry's development of large-scale hydroxyapatite nanoparticle production.

Computer simulation and optimization of the oxidation process in the production of nitric acid in the Aspen Plus environment

The article presents a method for determining the optimal technological and design parameters of the process, as well as the procedure for conducting technological analysis in the Aspen Plus environment. With the help of a wide range of thermodynamic models and process property databases, this modeling environment allows for an accurate representation of their behavior in the production of nitric acid. By using computer modeling in Aspen Plus, a 60.09% aqueous solution of HNO3 was obtained for 93465.8 kg/h of air and 5458.9 kg/h of ammonia. The objective of this modeling was to determine the optimal process parameters and its configuration, conduct a technological analysis, and determine the flows and properties of substances at various points. The main process parameters were analyzed, and their interrelation is shown in the graphs.

Improvements in ORR Activity and Cell Performance of Pt-Based Catalysts for PEFCs By Modification with Protonated Melamine-Derivative Salts

1. Introduction Improvement in ORR activity of Pt-based catalysts for use in PEFCs of FCVs is crucial for cost reduction and widespread use [1]. We reported that surface modification of Pt and Pt-based catalysts with melamine molecules enhances ORR activity [2, 3]. However, it is predicted that the melamine is easily washed off by water generated at the cathode in PEFCs because melamine is soluble in water. In this study, organic salts composed of protonated melamine derivatives and bis(nonafluorobutanesulfonyl)imide were newly synthesized to suppress the washing-off effects. Pt and Pd@Pt core-shell catalysts were modified with the organic salts, and the ORR activity and the I-V performance were investigated. 2. Experimental Ketjen Black EC-600JD (KB, SBET: 1,345 m2/g, LION) and mesoporous carbon (MPC, CNovel MH-18®, SBET 1,334 m2/g, TOYO TANSO) were used as carbon supports for Pd@Pt core-shell and Pt catalysts, respectively. The Pt/Pd/KB core-shell catalyst was synthesized by a direct displacement reaction method [4] and the Pt/MPC catalyst was synthesized by an impregnation/thermal reduction method. The organic salts were synthesized by mixing equimolar melamine derivatives and Li bis(nonafluorobutanesulfonyl)imide in 0.1 M HNO3 aqueous solution at 80oC. Pt/Pd/KB catalyst was loaded onto a glassy carbon electrode and immersed in acetone containing 0.1 mM organic salts for 10 min. to modify the catalyst surface with the organic salts. CV of Pt/Pd/KB catalyst was recorded at 25oC in Ar-saturated 0.1 M HClO4 with a potential scan rate of 50 mV/s and LSV was measured by RDE method at 25oC in O2-saturated 0.1 M HClO4 with a potential scan rate of 10 mV/s at a rotation speed of 1,600 rpm.Pt/MPC catalyst was dispersed in acetone containing 20 wt.% organic salt and acetone was slowly evaporated by using an evaporator to modify the catalyst with organic salt, and used for 1 × 1 cm2 MEA tests. The MEA was fabricated by a decal method using Nafion® membrane (25 µm in thickness) and a GDL (SGL). Nafion® DE2020 was used as an ionomer for catalyst ink preparation (I/C: 0.83). The Pt loading of the cathode catalyst layer in the MEA was set to 0.1 mg-Pt/cm2. I-V performance of the MEA was evaluated at 80oC, 75% RH. H2 gas (418 NmL) and air (998 NmL) were supplied to the anode and the cathode, respectively, and the H2 gas was pressurized to 150 kPa (ambient + 50 kPa) at the gas-outlet (H2 utilization: 5% at a current density of 3.0 A/cm2). 3. Results and Discussion Figure 1 shows molecular structure of an organic salt of [diethylmelamine+H]+[bis(nonafluorobutanesulfonyl)imide]- ([DEM]+[NFSI]-). The salt was synthesized in 0.1 M HNO3 (pH 1) at 80oC and was obtained in a solid state in the solution with a yield > 90%. CVs of Pt/Pd/KB catalyst and after modification with [DEM]+[NFSI]- are depicted in Figure 2. Hydrogen adsorption/ desorption waves observed in the potential range of 0.05-0.4 V were slightly suppressed by the modification, indicating that surface Pt active sites were partially occupied by the salt. Simultaneously, the onset potential for Pt-OH formation was positively shifted and the formation of Pt-oxygenated species was suppressed in the high potential range of 0.7-1.2 V, showing that the modified Pt surface retained more metallic state at high potentials. Figure 3 demonstrates LSVs of the Pt/Pd/KB catalyst and after modification with [DEM]+[NFSI]-. The LSV of the catalyst positively shifted by the modification and the ORR mass activity was enhanced from 1,223 to 2,234 A/g-Pt at 0.9 V. These results indicated that the modification of the Pt/Pd/KB catalyst with [DEM]+[NFSI]- was effective in enhancing ORR activity and the results are almost the same as the activity enhancement observed by melamine modification [3].Figure 4 shows I-V performance of the MEA using Pt/MPC as the cathode catalyst. The cell voltage of the MEA using the modified Pt/MPC exceeded that using the unmodified catalyst in the whole current density region, indicating that ORR activity enhancement by the organic salt modification was also demonstrated in the MEA tests. Furthermore, the resistance and the diffusion overpotentials as well as the activation overpotential were all reduced by the modification with [DEM]+[NFSI]-. Thus, the organic salt could interact with ionomers or membrane and decrease the resistance and the diffusion overpotentials.This study was partly supported by NEDO, Japan.

Extraction behaviors of platinum group metals from an aqueous HNO3 solution using ionic liquids containing a novel thiodiglycolamide-type extractant

Extraction behaviors of platinum group metals from an aqueous HNO3 solution using ionic liquids containing a novel thiodiglycolamide-type extractant

Effect of film thickness and morphology on photoelectrochemical performance of (001) orientated BiOBr thin films prepared via mist CVD

High-quality (001) orientated bismuth oxobromide (BiOBr) thin films were deposited on polycrystalline Sn: In2O3-glass substrates at open-air atmospheric pressure with mist chemical vapor deposition (CVD). Generally, it is difficult to control the surface morphology and thickness for BiOBr because of the high anisotropic crystal structure and very volatile halide. In this study, the growing thickness of BiOBr thin films showed a linear correlation with deposition time. Small thickness resulted in limited absorption ability, while large thickness led to increase of electrical resistance. The surface morphology of (001) orientated BiOBr thin films can be improved obviously under the acidic environment via suppressing Bi3+ hydrolysis. The (001) orientated BiOBr thin films that deposited by mixed solvent of DMF and 35% HNO3 aqueous solution exhibited the highest photocurrent density with 0.33 mA cm−2 at 0.6 V vs Ag/AgCl. The intermediate thickness and continuous surface morphology effectively promote the transfer and separation of electron-hole pairs, leading to superior photoelectrochemical (PEC) performance.

Eco-friendly dispersive liquid–liquid microextraction procedure based on solidification of floated organic drop coupled with back-extraction for preconcentration of rare earth elements

ABSTRACT In this study, a simple and efficient eco-friendly procedure for preconcentration of trace amounts of Y, Sm, Eu, Gd, Er and Yb was developed prior to determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The extraction process involved two sequential steps. The first is based on ultrasonic-assisted emulsification solidified floating organic drop microextraction using morin and 1-undecanol as complexing and extraction agents, respectively. The analyte in the solidified floated organic drop was then back-extracted into aqueous solution of HNO3 to prevent the relapsing effect of the organic matrix on the performance of ICP-OES. The effect of various experimental parameters on the extraction efficiency was studied and optimised. The limits of detection were in the range of 0.053 (Y) – 0.086 (Sm) µg L−1 with linear dynamic analytical range of 0.3–1000 µg L−1 at the optimal conditions. The relative standard deviations (C = 20 µg L−1, n = 10) ranged from 1.7% (Eu) to 2.5% (Yb). Finally, the approach represented high efficiency in determining the rare earth elements in certified reference material and phosphite rock samples.

Analysis of Techniques for Determining the Number of Electrons Exchanged in Square-Wave Voltammetry

A comparison of square-wave voltammetry models for calculating the number of electrons exchanged in a metal deposition reaction. Square-wave voltammetry is extremely useful for isolating the behavior of a single reaction in a mixed solution of many reacting species. Being able to identify the number of electrons exchanged in a reaction is extremely useful for identifying and characterizing unknown compounds in a process, such as electrorefining, molten salt reactors, and electrolytic oxide reduction. Experiments were conducted for silver deposition on platinum in an aqueous HNO3 solution and for Nickel and Lanthanum deposition on Tungsten in molten LiCl. Diffusion coefficients for Ni2+ and La3+ in LiCl at 700oC are calculated. Accuracy of the soluble-soluble model versus the soluble-insoluble model is discussed. Nucleation dynamics, natural convective and radial diffusive effects, and amount of ohmic drop compensation are all found to impact the resulting calculation for the number of electrons exchanged. A simplified model for determining the number of electrons exchanged under the constraint of well-compensated ohmic drop is proposed and evaluated.

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.

Synthesis and performance of a composite photocatalyst based on polyester-supported carbon nitride nanosheets for selective oxidation of anisyl alcohol

Heterogeneous photocatalysis represents an essential organic synthesis strategy for the sustainable development of new routes to the highly efficient production of fine chemicals. This work describes a coating method using polyester fibre (PES) to support carbon nitride nanosheets (GCN-TS). PES surface was treated with HNO3 aqueous solutions with different concentrations (0.2 – 5% v/v), which enhanced the adhesion of the GCN-TS on PES fibres. The surface of coated PES treated with 1% v/v HNO3 results in a homogeneous deposition of the photocatalyst and increased hydrophilicity. The photocatalytic synthesis of p-anisaldehyde by oxidation of anisyl alcohol in an aqueous solution assisted by 417 nm visible light-emitting diodes resulted in 95% yield operating in batch mode. The prepared material could be reused, maintaining its photocatalytic performance during five consecutive tests. Aiming at industrial processing, the synthesis of anisaldehyde was performed using the same catalyst in a continuous flow photocatalytic reactor. The performance of the process depends on the residence time of the mixture containing the reactant, as the contact with the immobilised photocatalyst determines the yield.