Experimental and numerical study on water sorption over modified mesoporous silica

–SO₃H modified mesoporous silica adsorbent with water sorption capacity and fast desorption kinetics for water sorption was synthesized and studied via a combined experimental and numerical approach. Mesoporous silica was synthesized using sol–gel method in H₂SO₄ medium. The water adsorption isotherms and kinetics over the silica were evaluated by a dynamic water vapor sorption analyzer. Mesoporous silica was modeled using annealing simulation with CVFF forcefield. –SO₃H modified mesoporous silica was modeled by the attachment of –SO₃H to the surface hydroxyl groups and validated. Simulation results show water sorption capacity at low relative humidity (RH) increases with –SO₃H loading on mesoporous silica. Energy distribution of intermolecular interaction and micro-view of water sorption over –SO₃H modified mesoporous silica reveal that although strong interaction (intermolecular interaction of ?40 to ?20 kcal/mol) between hydrophilic groups (–SO₃H) with water can increase water sorption capacity at low RH, weak H₂O–H₂O interaction (intermolecular interaction of ?20 to ?10 kcal/mol) dominated water sorption capacity at both low and high RH.     

Influence of pyridazine derivative on corrosion inhibition of mild steel in acidic media

The inhibition behavior of 6-methyl-4,5-dihydropyridazin-3(2H)-one (MDP) on corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ was investigated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The results indicated that the corrosion inhibition efficiency depends on concentration, immersion time, solution temperature, and the nature of the acidic solutions. It is also noted that MDP is at its the most efficient in 1 M HCl and least in 0.5 M H₂SO₄. The effect is more pronounced with MDP concentration. It is found that the inhibition efficiency attains 98 % at 5 × 10^?3 M in 1 M HCl and 75 % at 5 × 10^?2 in 0.5 M H₂SO₄. Polarization measurements showed that the MDP acts as a mixed inhibitor. EIS diagrams showed that the adsorption of MDP increases the transfer resistance and decreases the capacitance of the interface metal/solution. From the temperature studies, the activation energies in the presence of MDP were found to be superior to those in uninhibited medium. Finally, a mechanism for the adsorption of MDP was proposed and discussed.     

Enhanced Xylose Recovery from Oil Palm Empty Fruit Bunch by Efficient Acid Hydrolysis

Oil palm empty fruit bunch (EFB) is abundantly available in Malaysia and it is a potential source of xylose for the production of high-value added products. This study aimed to optimize the hydrolysis of EFB using dilute sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄) via response surface methodology for maximum xylose recovery. Hydrolysis was carried out in an autoclave. An optimum xylose yield of 91.2 % was obtained at 116 °C using 2.0 % (v/v) H₂SO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. A lower optimum xylose yield of 24.0 % was observed for dilute H₃PO₄ hydrolysis at 116 °C using 2.4 % (v/v) H₃PO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. The optimized hydrolysis conditions suggested that EFB hydrolysis by H₂SO₄ resulted in a higher xylose yield at a lower acid concentration as compared to H₃PO₄.     

A new acidic Ti sol impregnated kaolin photocatalyst: synthesis, characterization and visible light photocatalytic performance

In this study, a photocatalyst with visible light photocatalytic activity was obtained using raw materials, including commercial TiO₂, sulfuric acid, and calcined kaolin (CK). The photocatalyst was prepared via a dissolving/impregnating process, in which acidic Ti sol was obtained by initially dissolving TiO₂ particles in sulfuric acid, and then using the sol as impregnant for the CK. The prepared photocatalyst had wide spectral region and narrow band gap. In addition, the impregnation can create acid sites on the obtained composite surface and consequently improve the activity. A series of tests was performed to characterize the properties of the prepared samples. The visible light photocatalytic degradation of methyl orange (MO) in an aqueous solution was used as a probe reaction to evaluate the photocatalytic activities of the obtained samples. Under visible light irradiation, approximately 80 % of MO (with initial concentration of 20 mg/m³) was degraded in 3 h on the photocatalyst prepared by impregnating CK in acidic Ti sol, which was obtained using approximately 60 % H₂SO₄ solution followed by calcination at 400 °C. The acidity of the photocatalyst is the main factor that affects the catalytic activity of the photocatalytic degradation of MO.     

Synthesis,crystal structure,and blue photoluminescence of a 3D coordination polymer based on a Ag10 cluster with the versatile 2-mercapto-5-benzimidazolesulfonic acid ligand

The solvothermal reaction of 2-mercapto-5-benzimidazolesulfonic acid (H₃MBZD), which has imidazole, –SH, and –SO₃H groups, with Ag₂SO₄ led to the 3D coordination polymer {Ag₅[(HMBZD)₂(H₂MBZD)(H₂O)]} _n (1). X-ray single-crystal analysis showed that five independent Ag atoms are connected by the bridging mercapto group to generate asymmetric pentanuclear clusters, which are joined together to form a large Ag₁₀ ringed subunit. The Ag₁₀ subunits are linked together by the –SO₃H groups to give the complex 3D framework. Strong blue photoluminescence of 1 can be assigned to the intraligand fluorescent emission.     

Efficient hydrolyzation of cellulose in ionic liquid by novel sulfonated biomass-based catalysts

A green and effective approach for comprehensive hydrolyzation of cellulose has been described. Several carbon-based solid acids were successfully prepared using various biomass (glucose, microcrystalline cellulose, bamboo, and rice husk) and used to catalyze cellulose hydrolysis. The acid groups (–SO₃H and –COOH) were successfully introduced onto the surface of the carbon-based solid acid catalysts as evidenced by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The structure of the prepared catalysts was characterized by scanning electron microscope and X-ray diffraction. The catalysts showed excellent catalytic performance for hydrolysis of cellulose. To improve the reaction efficiency, ball-milling and solubilization in ionic liquids of cellulose were adopted. A maximum total reducing sugar yield of 81.8 % was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 125 °C for 90 min when the water addition was 10 % of ionic liquid. This study provided a promising strategy to synthesize solid acids from lignocelluloses, which were further used to convert biomass into biofuels and platform chemicals.     

The pH effects on the capacitive behavior of nanostructured molybdenum oxide

Nanostructured molybdenum oxide having a particle size in the range of 30–80 nm was prepared by potentiodynamic electrodeposition method, and the effects of H₂SO₄ concentration on its capacitive behavior were studied by cyclic voltammetry, galvanostatic discharge, and electrochemical impedance spectroscopy. Poor to fair capacitive behaviors were witnessed depending on the electrolyte concentration and conditions of charge/discharge. Increasing acid concentration to 0.02 M had favorable effect, while beyond that, the effect was detrimental. Capacitance around 600 F g^?1 was recorded in the potential range of 0 to ?0.55 V vs. Ag/AgCl.     

Cellulose hydrolysis catalyzed by highly acidic lignin-derived carbonaceous catalyst synthesized via hydrothermal carbonization

Acidic carbonaceous solids were synthesized from mass pine alkali lignin via hydrothermal carbonization followed by sulfonation. Hydrothermal carbonization of lignin in the presence of acrylic acid (LAHC-SO₃H) provided many more carboxylic groups than that in the absence of acrylic acid, allowing subsequent sulfonation to produce a highly active and stable catalyst for cellulose hydrolysis in the [BMIM]Cl-H₂O solvent system. The hydrochar and catalyst were characterized using field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, thermal gravimetric analysis, Fourier transform infrared spectrometer, Brunauer–Emmett–Teller and acid–base titration. Results showed that a high acid content of 5.48 mmol/g, including carboxylic group (2.85 mmol/g), phenolic hydroxyl group (1.05 mmol/g) and sulfonic acid group (1.58 mmol/g), contributed significantly to the highly efficient hydrolysis of cellulose. Further, it was found that addition of trace water in [BMIM]Cl was favorable to cellulose hydrolysis. The highest yield (75.4%) of total reducing sugar (TRS) obtained in [BMIM]Cl-H₂O at a mass ratio of 100:1 was more than twice that (36.1%) achieved in [BMIM]Cl without water; the corresponding reaction conditions were 50 mg of microcrystalline cellulose, 30 mg of catalyst, 1.0 g of [BMIM]Cl, 10 mg of H₂O, reaction temperature of 130 °C and reaction time of 2 h. Furthermore, the TRS yield with 5 cycles for LAHC-SO₃H was higher than 68.1%, and the catalytic activity of catalyst could be fully recovered (74.0% of TRS yield) easily by regeneration.     

Flue Gas Desulfurization by Dielectric Barrier Discharge

There are many problems with flue gas desulfurization by traditional gas ionization discharge, including the large size of the plasma source, high energy consumption, and the need for a traditional desulfurization method. This paper introduces oxidization of SO₂ to sulfuric acid (H₂SO₄) in a duct by reactive oxygen species (O₂ ⁺, O₃) produced by strong ionization dielectric barrier discharge. The entire plasma reaction process is completed within the duct without the use of absorbents, catalysts, or large plasma source. The reactive oxygen species O₂ ⁺ reacts with gaseous H₂O in the flue gas to generate ·OH radicals, which can oxidize trace amounts of SO₂ in large volumes of the flue gas to produce H₂SO₄. Sulfuric acid is also produced by O₃ oxidation of SO₂ to SO₃, and SO₃ reacting with gaseous H₂O in the flue gas. Experimental results showed that with a gas temperature of 22 °C and reactive oxygen species injection rate of 0.84 mg/L, the SO₂ removal rate was 81.4 %, and the SO₄ ^2? concentration in the recovered liquid H₂SO₄ reached 53.8 g/L.     

Hydroclathrus clathratus marine alga as a green inhibitor of acid corrosion of mild steel

The corrosion inhibitive and adsorption behaviors of Hydroclathrus clathratus on mild steel in 1 M HCl and 1 M H₂SO₄ solutions at 303, 313 and 323 K were investigated by weight loss, electrochemical, and surface analysis techniques. The results show that H. clathratus acts as an inhibitor of corrosion of mild steel in acid media. The inhibition efficiency was found to increase with increase in inhibitor concentration but to decrease with rise in temperature, suggestive of physical adsorption. The adsorption of the inhibitor onto the mild steel surface was found to follow the Temkin adsorption isotherm. The inhibition mechanism was further corroborated by the results obtained from electrochemical methods. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses supported the inhibitive action of the alga against acid corrosion of mild steel.     

A theoretical study on surface modification of a nanosized BC3 tube using C2H4 and its derivatives

Chemical functionalization of a BC₃ nanotube (BC₃NT) with C₂X₄ (X = –H, –F, –CH₂F, –CN, –NH₂, –NO₂, –CH₃, and –OCH₃) was investigated by density functional theory calculations. It was found that C₂H₄ prefers to be added to a B–C bond of the tube wall. The interaction energies are calculated to be ranging from ?0.03 to ?40.32 kcal/mol, and their relative magnitude order is found to be as follows: C₂F₄ > C₂(NH₂)₄ > C₂H₄ > C₂(NO₂)₄ > C₂(OCH₃)₄ > C₂(CN₄)₂ > C₂(CH₃)₄ > C₂(CH₂F)₄. For chemically modified BC₃NTs with various functional groups, the functionalization energy can be correlated with the trend of relative electron-withdrawing or electron-donating capability of the adsorbates. The calculated density of states shows that the functionalization of BC₃NT with these functional groups (except C₂(NO₂)₄) can be generally classified as a certain type of “electronically harmless modification”. We believe that the preservation of electronic properties of BC₃NTs coupled with the enhancement of solubility may render the chemical modification to be an effective way for the purification of BC₃NTs. The insight provided by this theoretical study may also assist future development of BC₃NTs with targeted chemoselectivity through chemical functionalization.     

MWCNTs/metal (Ni, Co, Fe) oxide nanocomposite as potential material for supercapacitors application in acidic and neutral media

Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H₂SO₄) and sodium sulphate (Na₂SO₄) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF?cm^?2 (ca 2,119 F?g^?1) in H₂SO₄. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.     

Fluorimetric estimation of U(VI) in the presence of a large excess of Th(IV)

A fluorescence based method has been developed for the determination of trace amounts of uranium in thorium matrix using a mixture of phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄), as fluorescence enhancing reagent for uranyl (UO₂ ²⁺) ion fluorescence. Synthetic samples mimicking the composition of ThO₂ fuel were prepared and the concentration of U(VI) was estimated. Satisfactory results are obtained when uranium is present at a concentration of 10 ppm in solid thorium samples with good precision.     

Comparative potentiality of Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax) as lignocellulosic feedstocks for the release of monomeric sugars by microwave/chemical pretreatment

Two-stage microwave (microwave/NaOH pretreatment followed by microwave/H₂SO₄ pretreatment) was used to release monomeric sugars from Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax). The optimum pretreatment conditions were investigated, and the maximum monomeric sugar yields were compared. The microwave-assisted NaOH and H₂SO₄ pretreatments with a 15:1 liquid-to-solid ratio were studied by varying the chemical concentration, reaction temperature, and reaction time to optimize the amount of monomeric sugars. The maximum amounts of monomeric sugars released from microwave-assisted NaOH pretreatment were 6.8 g/100 g of biomass [at 80 °C/5 min, 5 % (w/v) NaOH for S. spontaneum and at 120 °C/5 min, 5 % (w/v) NaOH for A. donax]. Furthermore, the maximum amounts of monomeric sugars released from microwave-assisted H₂SO₄ pretreatment of S. spontaneum and A. donax were 33.8 [at 200 °C/10 min, 0.5 % (w/v) H₂SO₄] and 31.9 [at 180 °C/30 min, 0.5 % (w/v) H₂SO₄] g/100 g of biomass, respectively. The structural changes of S. spontaneum and A. donax were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy.     

Electrochemical behaviors and determination of melamine in neutral and acid aqueous media

The electrochemical behaviors of melamine (MEL) were studied at paraffin-impregnated graphite electrode in PBS (pH 7.0) and 0.5 M H₂SO₄. Various methods including UV–vis thin-layer spectroelectrochemistry, infrared spectra (IR) and electrochemicatry have been performed to investigate the characteristics. In 0.1 M PBS (pH 7.0), MEL loses two electrons to form a dication, which couples head-to-head with a neutral molecule of MEL to form a dimer accompanying the production of azocompound, the dimer plays a role of a monomer in the following polymerization. In 0.5 M H₂SO₄, unstable MEL mostly hydrolyzes to form ammeline, ammelide, s-triazine-2,4,6-trion, and tricyanic acid, respectively; The hydrolysis could be accelerated by electrochemical method; Meanwhile, MEL associates tricyanic acid to give a plane molecule cake by hydrogen bonding. The spectra responses of MEL at 205 and 234 nm are linearly increasing in a same concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻⁵ M in 0.5 M H₂SO₄ (determination limit, 1 × 10⁻⁸ and 3 × 10⁻⁸ (3σ)). The proposed method was successfully applied to the determination of MEL in real sample.

     

Enhancement inhibition efficiency of PBTCA depending on the inclusion complex with hydroxypropyl-β-cyclodextrin

For the first time, hydroxypropyl-β-cyclodextrin (HP-β-CD) has been brought in to include 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) in order to enhance inhibition efficiency of PBTCA, which leads a new approach to study oil–gas field corrosion inhibition in the process of acid treatment. Based on the host–guest inclusion reaction, the inclusion complex of PBTCA with HP-β-CD has been prepared in the laboratory. UV–Vis absorption spectrum was applied to study the inclusion behavior of PBTCA with HP-β-CD. The results revealed that PBTCA with HP-β-CD can form a 1:1 stoichiometry inclusion complex. The 1:1 inclusion complex synthesized by using lyophilization was further characterized by Fourier transform infrared spectroscopy. Besides, inhibition effect of the inclusion complex on the corrosion inhibition of Q235 carbon steel has been investigated in 0.1 M sulfuric acid (H₂SO₄) solution using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and scanning electron microscopy (SEM). It was found that the presence of the inclusion complex better achieved the anti-corrosion property in aggressive medium than was the case with alone PBTCA and the highest inhibition efficiency of the inclusion complex over 90 % was obtained, which are suggestive of the active effect of the inclusion complex for improving inhibition efficiency of PBTCA. Meanwhile, the results obtained from SEM further showed that the inclusion complex acts as a more efficient corrosion inhibitor for Q235 carbon steel in H₂SO₄ medium.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

Novel hybrid process for the conversion of microcrystalline cellulose to value-added chemicals: part 1: process optimization

In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H₂SO₄ was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H₂SO₄ concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H₂SO₄).     

Active carbon supported S-promoted Bi catalysts for acetylene hydrochlorination reaction

We synthesized a S doped Bi/AC catalyst for acetylene hydrochlorination. The addition of H₂SO₄ changes the structure of the Bi atoms in the catalyst, resulting in the improvement of the specific surface areas and catalytic efficiency of the Bi-based catalyst under reaction conditions.     

Selective conversion of cellulose to levulinic acid and furfural in sulfolane/water solvent

Direct conversion of cellulose into levulinic acid and furfural in sulfolane media with the aid of water and H₂SO₄ was performed at 140–220 °C under the pressures of 0–1.5 MPa. This approach could obtain 72.5 mol% levulinic acid and 11.5 mol% furfural formation under an optimal condition in which the mass ratio of sulfolane, water and H₂SO₄ was 90:10:1. It was found that the decrease of water content led to an increasing yield of furfural and that the maximum furfural yield (51.1 mol%) could be obtained in the absence of water. The synergism of sulfolane and water in the selective liquefied system was demonstrated to be responsible for not only reinforced effect of optimizing and isolating the target products but also for reducing re-polymerization and side reactions. Furthermore, sulfolane in our case could be recycled and re-used for the conversion of cellulose with the same yield, which shed light on the remarkable potential for future industrial application.