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The present work demonstrates the degradation of two persistent and highly toxic organophosphorus pesticides, i.e. monocrotophos (MCP) and quinalphos (QP), which are an inevitable part of Indian agricultural practices. The major emphasis lies in using the naturally and easily available, inexpensive sunlight for water purification. Thus, TiO2 was modified into sulphur-doped TiO2 (S–TiO2) to make it active under sunlight via wet impregnation method. Various catalysts were synthesized by varying the dopant ratio and characterized using FESEM, EDS, XRD, UV-DRS and TEM. With doping, a significant decrease in band gap energy from 3.2 to 2.9 eV was noticed. FESEM revealed that the particles are spherical shaped and slightly agglomerated. Particle size was found to decrease from 33 nm for P25 to 26.82 nm for doped TiO2. According to the various results obtained, 0.7:1 (S:Ti) dopant ratio catalyst was concluded to give optimum results. Further, the degradation studies were carried out under sunlight by varying and optimizing various parameters, i.e. dopant concentration, calcination temperature, catalyst loading, pH and initial concentration. Maximum degradation of 95.36% and 98.09% for MCP (25 mg/L) and QP (20 mg/L) is obtained, respectively, with 0.7:1 (S:Ti) as optimum dopant ratio. Kinetics was studied using Langmuir–Hinshelwood–Hougen–Watson (LHHW) model and was found to obey pseudo-first-order kinetics. The mineralization of pesticides into simpler compounds was confirmed by COD analysis and degradation pathway is also proposed for both the pollutants. [ABSTRACT FROM AUTHOR]

The study aims at quantifying the effect of fluid elasticity on frictional pressure drop for the flow of viscoelastic fluid through a helical coil. Aqueous solutions of polyacrylamide (PAA) in the concentration range 0.25 %–0.5 % (wt/vol.) were used as test fluids. The fluids were characterized using dynamic rheometer under rotational and oscillatory modes. The rheological study depicts that the fluids exhibit elasticity and shear thinning behavior. Experimental data on pressure drop for the flow of non-Newtonian viscoelastic fluid through a helical coil have been generated. Drag enhancement was observed for the fluids with significant elastic character. An existing correlation applicable over a wide range of Germano number (NGn) for the flow of Newtonian fluids through helical coils (11.7≤Dc/dt≤105.48, 8.3≤p/Dt≤66.7), proposed by Gupta et al.22, has been extended to non-Newtonian viscoelastic fluids by incorporating the effect of fluid elasticity in terms of Weissenberg number (We). The proposed model’s uncertainty has been reported for 95 % confidence to assess the significance of newly reported results. The observed data were compared with the available models in the literature statistically using mean relative quadratic error (MRQE) and arithmetic relative error (%ARE). Lower values of MRQE and %ARE depict the acceptability of the proposed model. [ABSTRACT FROM AUTHOR]

The esterification of free fatty acids (FFA) in rice bran oil (RBO) with methanol in the presence of sulfuric acid as a homogeneous catalyst was studied. The effects of catalyst concentration (0.15 to 1.0 wt%), reaction temperature (318 K to 333 K), and molar ratio of oil to methanol (1:5 to 1:30) on the conversion of FFA were investigated to optimize the conditions for maximum conversion of FFAs. A detailed kinetic study was carried out using second-order pseudo-homogeneous kinetic model. The kinetic parameters were obtained and activation energy was determined from the Arrhenius plot. The activation energy of 23.21 kJ mol-1 and pre-exponential factor of 32.65 L mol-1 min-1 was obtained under the optimum catalyst concentration of 0.5 wt %, stirring speed of 500 rpm and oil to methanol ratio 1:20. [ABSTRACT FROM AUTHOR]

The present study describes the synthesis of crosslinked chitosan (CS) hydrogel beads with chemical crosslinkers (glutaraldehyde and epichlorohydrin) and natural crosslinking reagent (genipin). Crosslinking was carried out for 24 h in case of glutaraldehyde and genipin and for 2 h in case of epichlorohydrin with constant stirring and heating at 30°C. Swelling study of crosslinked chitosan hydrogel beads was carried out in SIF (simulated intestinal fluid) and SGF (simulated gastric fluid) medium followed by diameter increase ratio (DIR). Increased swelling of hydrogels, under acidic conditions, was due to the protonation of primary amino groups on chitosan, as confirmed by FTIR analysis. Surface texture of hydrogel beads was analyzed by scanning electron microscopy (SEM), which revealed that crosslinked beads had smooth surface compared to non-crosslinked beads. Thermogravimetric analysis (TGA) suggested genipin crosslinked CS beads with highest thermal stability. The use of these hydrogels for drug release was studied using amoxicillin as the model drug. Release studies carried out in SGF showed the release mechanism to be anomalous in nature and suggested potential of these hydrogels in controlled drug delivery devices. [ABSTRACT FROM AUTHOR]

Hydrogel films of Chitosan (CS) and Xanthan gum (XA) of compositions 100/0, 90/10, 80/20, 70/30, 60/40 and 50/50 (w/w) % were prepared and swollen in simulated gastric fluid (SGF) of pH 1.2 and simulated intestinal fluid (SIF) of pH 7.4. To impart stability in acidic environment, semi-interpenetrating polymer network (semi-IPNs) films were formed using glutaraldehyde (GA) as the crosslinking agent. With increase in XA concentration, equilibrium degree of swelling reduced in SGF as well as SIF indicating maximum intermolecular interactions for 50/50 CS/XA semi-IPN. The swelling data was observed to follow second order kinetics. Spectroscopic and thermal analyses of these semi-IPN films also suggest maximum intermolecular interactions for 50/50 CS/XA semi-IPN. The potential of using 50/50 semi-IPN in drug delivery was studied using amoxicillin. In-vitro drug release studies indicated higher drug release in SGF than in SIF suggesting dependence of amoxicillin release kinetics and diffusion coefficient on pH of the environment and drug loading. The results suggest that CS-based semi-IPNs with different crosslinker and XA concentration could be promising candidates for formulation in oral gastrointestinal delivery systems. [ABSTRACT FROM AUTHOR]

Methyl pentanoate, commonly known as methyl valerate, is the methyl ester of pentanoic acid (valeric acid) with a fruity odour. Methyl pentanoate is commonly used in fragrances, beauty care, soap, laundry detergents at levels of 0.1 - 1 %. In its very pure form (purity 99.5 %) it is used as a plasticizer in the manufacture of plastics. In the present investigation, kinetics of esterification of pentanoic acid with methanol catalyzed by heterogeneous catalyst in a batch-type reactor is reported. The effect of reaction conditions such as temperature, molar ratio, catalyst loading, and initial concentration of pentanoic acid and methanol, and the inhibiting effect of water on the kinetics has been studied. The pentanoic acid conversion reached 93 % at 333.15 K at a methanol to pentanoic acid molar ratio of 10:1 with 7 % (g L-1) Amberlyst 15 as catalyst. Mass transfer effects were found to be negligible. Observed reaction rate data was fitted to the regression technique. Estimated Eley-Rideal kinetic model reaction rate constants were fitted to the Arrhenius type equation with activation energy EA 39.5 kJ mol-1 and pre exponential factor ko 1.8 · 10³ L² g-1 mol-1 h-1. [ABSTRACT FROM AUTHOR]

A comprehensive kinetic investigationof the esterification ofnonanoic acid with 1-propanol in the liquid phase was carried outusing Amberlyst 15. Kinetic experiments were conducted using a batchreactor system at a stirrer speed of 500 rpm over the temperaturerange 323.15 −363.15 K. The catalyst loading was varied from4% (w/v) to 8% (w/v), and acid to alcohol molar ratios of 1:1, 1:5,1:10, and 1:15 were used. It was found that both external and internaldiffusion limitations did not affect the overall reaction rate. Theconversion of nonanoic acid increased with increasing temperatureand catalyst loading. The Eley–Rideal (E–R) model wastested to correlate the kinetic data, and the activity coefficientswere estimated using the UNIFAC model to account for the nonidealthermodynamic behavior of reactants and products. The model predictedthe kinetic behavior of the studied system reasonably well. Waterwas found to be more strongly adsorbed than other species presentin the system. The activation energy, preexponential factor, and standardenthalpy for the esterification was estimated to be 55.4 kJ/mol, 2.3× 105L2g–1mol–1h–1, and −218.08 J·mol–1, respectively, by this model. The influence of alcoholcarbon chain length was studied, and their effects on reaction kineticswere compared. It was observed that activation energy increases withincreases in chain lengths of alcohols. [ABSTRACT FROM AUTHOR]

Hydrogels based on Poly(vinyl alcohol)(PVA), poly(ethylene oxide)(PEO) and Xanthan Gum(XG) cross linked with 25% (w/v) aqueous solution of Glutraldehyde (GA) were prepared. The effect of initial PVA/ PEO, PVA/XG weight ratio and the effect of amount of crosslinker (GA) on the dynamic and equilibrium swelling behaviour of the hydrogels was investigated. Hydrogels were characterized by percentage swelling, the polymer volume fraction in the swollen state, effective molecular weight of the polymer chain between two neighbouring crosslinks, mesh size and compressive strength. It was observed that the swelling capacity of the hydrogels decreases with increasing amount of crosslinker. The results show a significant influence of PEO and XG concentrations on the swelling behaviour of the PVA/PEO and PVA/XG hydrogels respectively. Hydrogels with higher PEO content had a higher percentage swelling mainly because of its hydrophilic nature and the percentage swelling was higher at pH 3.0 than at pH 7.4. On the other hand, addition of XG to PVA results in decrease in the swelling capacity of PVA/XG hydrogels. XG was found to add strength to the PVA/XG hydrogels. [ABSTRACT FROM AUTHOR]

Poly(acrylamide-co-acrylic acid) hydrogels, poly(AAm-co-AAc), were synthesized by free radical polymerization in solution using N,N'-methylenebisacrylamide (MBAAm) as the crosslinker. The structural parameters and the swelling behavior of the synthesized hydrogels were investigated for varying nominal crosslinking ratio and composition of the hydrogels. The use of hydrogels for drug release was investigated with gentamicin sulfate (GS) as the model drug. The drug release from hydrogels was investigated as a function of hydrogel composition, nominal crosslinking ratio (X) and drug loading. The observed drug release data was fitted to a power law model and the power law exponent (n) suggested that the drug release mechanism from these hydrogels was sensitive to hydrogel composition and was swelling-controlled for low concentrations of AAc and showed Fickian diffusion for high concentrations of AAc in the hydrogels. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies were performed on control hydrogel samples and drug loaded hydrogels to understand the chemical interactions between the drug and the polymer. Specific drug interactions were observed in these hydrogels. [ABSTRACT FROM AUTHOR]

In the present work, hydrogels based on acrylamide (AAm) and acrylic acid (AAc), crosslinked with N,N’-methylenebisacrylamide (MBAAm) were prepared by free radical polymerization in solution. The effect of initial AAm/AAc mole ratio and nominal crosslinking ratio (moles of crosslinking agent/moles of polymer repeat unit) on the dynamic and equilibrium swelling behaviour of hydrogels was investigated. Hydrogels were characterized by the polymer volume fraction in the swollen state (V2,s ), the number average molecular mass between crosslinks (Mc ) and the mesh size (ϵ). The swelling capacity of hydrogels was found to decrease with increasing nominal crosslinking ratio. The results show a significant influence of AAc monomer concentration on swelling behavior of poly(acrylamide-co-acrylic acid) hydrogels. Hydrogels containing higher acrylic acid content had a higher equilibrium mass swelling at pH 7.4 and in distilled water than at pH 3.0 where the acrylic acid is present in nonionized state. Further, swelling data was fitted to various models and model parameters were evaluated using regression technique. Model analysis indicated that the swelling transport followed non-Fickian mechanism. Scanning electron microscopy (SEM) revealed the macroporous surface morphology of the matrix with pore size varying between 2–64 microns depending on the amounts of AAc in the hydrogel. [ABSTRACT FROM AUTHOR]