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In the present work, the mechanism behind the functioning of the eco-friendly dye-sensitized solar cell was explored. Dye-sensitized solar cells were fabricated using natural dyes extracted from common pear (Opuntia dillenii) and red tamarind (Tamarindus indica), and 1:1 mixture. Betalain and anthocyanin were identified as the main pigments that sensitize the semiconductor TiO 2 film. The best conversion efficiency of 0.47 % was achieved from betalain dyes and 0.14 % from anthocyanin dyesensitized solar cell [under standard Air Mass 1.5 illumination (85 mW cm -2 )]. The mixture of dye (1:1 mixture) adsorbed onto TiO 2 exhibited an efficiency of 0.20 %. The light absorption behavior of extracted dyes was studied using ultraviolet-visible analysis. The influence of the binding nature of the dyes with TiO 2 surface on the efficiency of the solar cells was analyzed through Fourier transform infra-red analysis. The electrochemical impedance spectroscopy was used to find out the internal charge transfer resistance of the cells. The device incident photonto-current efficiency was obtained from 5 to 25 % for different natural dyes and found to coincide with the photocurrent-voltage characteristics and electrochemical impedance spectroscopy analysis. Graphical Abstract

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The sorption characteristics and ion exchange behaviour of polyaniline picrate (PANIPI) with various sodium salts (NaF, NaCl, NaBr, NaNO2, NaNO3, NaClO4, Na2SO4, NaH2PO4, NaOH, Na2CO3 and NaHCO3) have been studied. Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm models are tested to describe the equilibrium established between PANIPI resin and solutions of sodium salt. The correlation coefficients show that Langmuir, Freundlich and Temkin models fit well for this sorption process. The sorption constants and negative ∆G° values indicate that the sorption of sodium salts on PANIPI is a favourable process. The ion exchange capacity (IEC) of the pristine PANIPI with these salts lie in the range of 1.96-3.49 meq/g and the separation factor (α) vary between 0.71-3.88 for the sodium salts used in the present study. These parameters indicate the suitability of PANIPI as a good ion exchanger. The UV-visible and FT-IR spectral changes before and after sorption are analysed to explain the sorption mechanism. The sorption capacities determined from the batch experiments are in the range 80-100 % for the sodium salts. The regenerative ability of PANIPI resin is ascertained from the column experiments conducted in three cycles. PANIPI is also found to possess antibacterial and antifungal activities. Hence, this novel chromogenic PANIPI resin has potential applications in desalination and ion detection processes.

Due to the weathering of rocks, effluents from industries and geochemical responses the fluoride interacts with the ground water. Precipitation, adsorption, ion-exchange, membrane process techniques helps to process defluoridation in water. Among these fluoride removal strategies, adsorption technique is direct, reasonable, and appropriate for drinking water treatment. A few adsorbents, for example, activated carbon and alumina, agricultural and industrial wastes etc., were endeavor the permissible range of fluoride availability in water by adsorption technique. Use of plant related materials and agricultural wastes as adsorbents are commonly involved in adsorption technique since these materials are easily available with biodegradable nature and also they are inexpensive materials. The principle reason for this literature survey is to give new thoughts regarding the defluoridation in aqueous solutions by adsorption method which was analyzed by numerous analysts. In this review paper, different adsorbents has been reviewed and their adsorption efficiency based on pH, initial fluoride concentration, temperature, contact time has been analysed. It is obvious from the review that the various adsorbents have demonstrated incredible capability of defluoridation. Be that as it may, at present there is an earnest requirement for the identification and improvement of progressively novel adsorbents which depends on economic and innovative aspects.