The dual role of palladium in enhancing the photocatalytic activity of CdS dispersed on NaY-zeolite.

A stable photocatalyst, CdS dispersed on zeolite with Pd as both the dopant and the co-catalyst, has been developed. Enhancement of photocatalytic activity for hydrogen generation is observed for CdS when doped with palladium and dispersed on NaY-zeolite (CdPdS-Z). A further increase in the photocatalytic activity of CdPdS-Z is observed when palladium is added as a co-catalyst (Pd-CdPdS-Z). Cd0.95Pd0.05S-Z is synthesized via a facile soft chemical route and the Pd co-catalyst is loaded onto the composite using a wet impregnation method. This composite catalyst exists as two phases consisting of CdPdS and zeolite and CdPdS exists as a highly dispersed phase on zeolite as revealed by TEM studies. The Pd doped CdS-zeolite composite exhibits increased visible light absorption indicating the alteration of the band structure of CdS as a result of doping. Time resolved fluorescence studies reveal that the lifetime of the charge carriers is higher in the composites than in pure CdS. A detailed characterization using XRD, Raman and X-ray photoelectron spectroscopy indicates that Pd has substituted for Cd in the CdS lattice and Pd exists in the Pd(2+) oxidation state. Solid state MAS NMR studies indicate that an interaction exists between CdS (or CdPdS) and zeolite at the interface and Cd selectively interacts with Al of the zeolite framework. The photocatalytic activity of the Pd-CdPdS-Z catalyst remains unchanged with repeated cycles. Characterization of the used catalyst indicates that it is stable under the present experimental conditions. The enhanced photocatalytic activity of Pd-CdPdS-Z is attributed to the enhanced visible light absorption arising due to Pd doping and increased lifetime of the photogenerated charge carriers assisted by zeolite and the Pd co-catalyst. This study highlights the multiple roles played by palladium in enhancing the photocatalytic activity of the CdS-zeolite composite.

Management of pellucid marginal corneal degeneration with rigid gas permeable contact lenses.

PURPOSE: To study the clinical performance of rigid gas permeable contact lenses (RGPCL) in patients with pellucid marginal corneal degeneration (PMCD). METHODS: This retrospective study consisted of 15 patients with clinical PMCD, confirmed by videokeratography (TMS-1, Computed Anatomy, Inc., New York, NY). Information collected from the medical records included patient demographic data, uncorrected visual acuity, refraction, best-corrected spectacle visual acuity, and topographic details, including kerotometry. Twenty-seven of 30 eyes were subjected to several contact lens trials using polymethylmethacrylate (PMMA) contact lenses, using a systematic and consistent approach. After successful contact lens trials, data regarding number of trials, trial time, final contact lens choice parameters, and best-corrected contact lens visual acuity were noted for each patient. During follow-up, visual acuity with RGPCLs, lens fit, and average wearing time were noted. RESULTS: Fifteen patients (30 eyes) with typically inferiorly located pellucid marginal corneal degeneration were included in this study. There were 12 men and 3 women, with a mean age of 39.73 years. Twenty-seven eyes of 15 patients were identified as subjects for multiple contact lens trials, and 24 (88.8%) eyes were successfully fitted with RGPCLs. Best-corrected visual acuity of 6/12 or better with spectacles was achieved in 14 (46.66%) eyes. The average astigmatism was -8.56D, and a majority of the patients with PMCD who were in the contact lens trial had an against-the-rule astigmatism (63.3%). The mean trial time for attempted eyes (i.e., patients with PMCD who successfully underwent the contact lens trials) was 77.7 minutes, and the number of trials required to finalize the choice of contact lenses ranged between 2 and 7. The median base curve for RGP lenses was 7.57, and median diameter was 10.00 mm. Best-corrected visual acuity of 6/12 or better with the final contact lens was achieved in 95.4% of the subjects. After an average follow-up of 22.91 months, one patient was lost to follow-up, and 2 eyes required discontinuation of the contact lenses. The average wearing time among the contact lens wearers at their last follow-up visits was 9.58 hours. Final visual acuity of 6/12 or better was observed in 77.3% of eyes at the end of 22.91 months. CONCLUSION: Large-diameter RGPCLs are better tolerated and lead to significant improvement in visual acuity in inferior PMCD.

Ophthalmic complications and management of Stevens-Johnson syndrome at a tertiary eye care centre in south India.

PURPOSE: To review the possible aetiological factors, ocular complications and their management in patients of Stevens-Johnson syndrome with ocular involvement, seen at a tertiary eye care centre. METHODS: We retrospectively reviewed the medical records of patients with Stevens-Johnson syndrome seen between 1987-1998 at L V Prasad Eye Institute. The demographic and possible aetiological factors data causing Stevens-Johnson syndrome were collected. The details of the ocular examination and treatment were collected and examined to determine the pattern of presentation, complications, treatment response and outcome. RESULTS: A total of 95 patients, 40 males (42.10%) and 55 females (57.89%), were identified during the 11-year period. A majority of the patients (n = 53; 55.78%) were between 20 and 40 years of age. All patients had bilateral involvement and most (n = 93; 97.89%) had bilateral symmetrical presentation. The duration from the onset of symptoms to the time of presentation at the institute varied from 6 days to 18 years with most patients presenting after one year (n = 39; 41.05%). The most commonly identified possible causative factor was drugs (n = 55; 51.89%). No definitive cause was identified in 37 (38.94%) patients, and 3 (3.15%) patients had a history of viral fever preceding the onset of Stevens-Johnson syndrome. The best corrected visual acuity at initial presentation was 6/12 or better in 32 (33.68%) patients. Lid abnormalities were observed in 87 (91.51%) patients, conjunctival abnormalities in 92 (96.84%) and corneal complications in 93 (97.89%). All patients were managed medically and 26 (27.36%) patients underwent surgery. CONCLUSION: Stevens-Johnson syndrome remains an important cause of severe visual loss and ocular morbidity, both of which significantly affect the quality of life. Not many medical or surgical options are available even in tertiary eye-care centres. Future advances in immune modulation techniques may prevent many of the sequelae that continue to occur despite the best possible medical care.