Sol–gel synthesis of DyCrO3 and 10% Fe-doped DyCrO3 nanoparticles with enhanced photocatalytic hydrogen production abilities

DyCrO₃ and 10% Fe-doped DyCrO₃ nanoparticles have been synthesized using a sol–gel method to investigate their performance in photocatalytic hydrogen production from water. The synthesized nanoparticles have been characterized by performing X-ray diffraction, energy dispersive X-ray spectroscopy and UV-visible spectrophotometric measurements. In addition, field emission scanning electron microscopy has been performed to observe their size and shape. The Fe-doped DyCrO₃ nanoparticles show a significantly smaller band gap of 2.45 eV compared to the band gap of 2.82 eV shown by the DyCrO₃ nanoparticles. The Fe-doped DyCrO₃ nanoparticles show better photocatalytic activity in the degradation of rhodamine B (RhB) compared to the photocatalytic activity shown by both the DyCrO₃ and Degussa P25 titania nanoparticles. The recycling and reuse of Fe-doped DyCrO₃ four times for the photo-degradation of RhB shows that Fe-doped DyCrO₃ is a stable and reusable photocatalyst. To evaluate the extent of the photocatalytic hydrogen production ability of the synthesized nanoparticles, a theoretical model has been developed to determine their “absorptance”, a measure of the ability to absorb photons. Finally, 10% Fe-doped DyCrO₃ proves itself to be an efficient photocatalyst as it demonstrated three times greater hydrogen production than Degussa P25.

DyFe_0.1Cr_0.9O₃ nanoparticles calcined at 700 °C demonstrate superior photocatalytic ability compared to that of DyCrO₃ nanoparticles calcined at the same temperature.

Effect of channeling agents on the release pattern of theophylline from kollidon SR based matrix tablets

The purpose of the present study was to investigate the effect of channeling agent on the release profile of theophylline from Kollidon SR based matrix systems. Matrix tablets of theophylline using Kollidon SR which is plastic in nature were prepared by direct compression process. NaCl and PEG 1500 were used as channeling agents. Drug release study was evaluated for eight hours using USP 22 paddle-type dissolution apparatus using distilled water as the dissolution medium. The release mechanisms were explored and explained with zero order, Higuchi, first order and Korsmeyer equations. The release rate, extent and mechanisms were found to be governed by the type and content of the channeling agents. Increased rate and extent of the drug release were found by using higher content of channeling agent (42.49%) in the matrix due to increased porosity when compared with the formulation having no channeling agents. On the other hand decreased rate and extent of drug release were observed in the formulation having lower channeling agent content (19.76%). PEG 1500 ensures maximum release of drug from Kollidon SR than NaCl when other parameters were kept unchanged. It was found that type and amount of channeling agent significantly affect the time required for 50% of drug release (T50%), percentage drug release at 8 hours, release rate constant (K) and diffusion exponent (n). Kinetic modeling of dissolution profiles revealed drug release mechanism ranges from diffusion controlled or Fickian transport to anomalous type or non-Fickian transport, which was mainly dependent on the type and amount of channeling agents. These studies indicate that the proper balance between a matrix forming agent and a channeling agent can produce a drug dissolution profile similar to a desired dissolution profile.

Effect of Channeling Agents on the Release Profile of Theophylline from METHOCEL K4M Based Matrix tablets

The present study was undertaken to investigate the effect of channeling agents on the release profile of Theophylline from METHOCEL K4M based matrix systems. Matrix tablets of Theophylline using METHOCEL K4M were prepared by direct compression process. METHOCEL K4M polymer is hydrophilic in nature. NaCl and PEG 1500 were used as channeling agents. Drug release study was evaluated for eight hours using USP 22 paddletype dissolution apparatus using distilled water as the dissolution medium. The release mechanisms were explored and explained with zero order, Higuchi and Korsmeyer equations. The release rate, extent and mechanisms were found to be governed by channeling agent type and content. Higher channeling agent content (42.49%) in the matrix increased the rate and extent of the drug release because of increased porosity in the tablet matrices, at lower channeling agent (19.76%) level, the rate and extent of drug release was decreased and in absence of channeling agents these were least. NaCl ensures maximum release of drug from low viscosity grade METHOCEL K4M than PEG 1500 when other parameters were kept constant. It was found that type and amount of channeling agent significantly affect the time required for 50% of drug release (T50%), percentage drug release at 8 hours, release rate constant (K) and diffusion exponent (n). Kinetic modeling of dissolution profiles revealed drug release mechanism ranges from diffusion controlled or Fickian transport to anomalous type or non-Fickian transport, which was mainly dependent on the presence of type and amount of channeling agent. These studies indicate that the proper balance between a matrix forming agent and a channeling agent can produce a drug dissolution profile similar to a theoretical dissolution profile.Key words: Channeling agent, Theophylline, Release Profile, Methocel K4MDOI = 10.3329/dujps.v7i1.1214Dhaka Univ. J. Pharm. Sci. 7(1): 27-32, 2008 (June)

Preparation and In vitro Evaluation of Theophylline Loaded Gastroretentive Floating Tablets of METHOCEL K4M

This investigation describes the preparation and in vitro evaluation of gastroretentive floating tablets of theophylline. Hydrophilic polymer METHOCEL K4M was used for its gel forming and release controlling properties. Sodium bicarbonate and citric acid were incorporated as gas generating agents. The effects of soluble components (sodium bicarbonate and citric acid), gel forming agent (METHOCEL K4M) and dose variation on drug release profile and floating properties were investigated. It has been observed that in all cases increase of the amount of floating agent caused a decrease of the floating lag time. Increase of theophylline load showed an increase of the floating lag time, which was independent of floating agent content. The release mechanisms were explored and explained with zero order, first order, Higuchi, Korsmeyer and Hixon-Crowell equations. The release rate, extent and mechanisms were found to be governed by the content of polymer and floating agent. The content of active ingredient was also a vital factor in controlling drug release pattern. It was found that polymer content and amount of floating agent significantly affected the time required for 50% of drug release (T50%), percentage drug release after 8 hours, release rate constant, and diffusion exponent (n). Kinetic modeling of dissolution profiles revealed that the drug release mechanism could range from diffusion controlled to case II transport, which was mainly dependent on presence of relative amount of theophylline, polymer and floating agent. Key words: Gastroretention, Floating tablet, Theophylline  DOI = 10.3329/dujps.v7i1.1220 Dhaka Univ. J. Pharm. Sci. 7(1): 65-70, 2008 (June)