A low cost linear parabolic concentrator system-photoreactor for photocatalytic processes that uses natural solar light

PdS/CdS based photocatalysts exhibit high efficiency in water splitting reaction. Due to the fact that the band gap value of CdS is 2.4 eV, the photocatalytic process may be performed using visible light at temperatures between 20 and 80°C. From our previous work we noticed that the yield of water splitting process, using this type of photocatalysts increases with the increase of temperature from 20 to 60°C. To increase the temperature of the photocatalystsuspension at higher values than the environment temperature, an irradiance greater than 1000 W/m2 is needed. In this paper we present the design and construction of an inexpensive solar collector –photoreactorassembly, by which the optimal temperature of photocatalystsuspension can be maintained,even in low solar irradiance conditions

The influence of cadmium precursors upon PdS/Zn1-XCXS photocatalysts efficiency in watersplitting reaction

Photocatalysts based on hexagonal cadmium sulfide have been hydrothermally synthesized using crystalline zinc sulfide as sulfide source, and metal nitrates, acetates, chlorides and sulfatesas cadmium sources. The powders have been characterized by X-Ray Diffraction (XRD), UV-VIS Diffuse Reflectance Spectroscopy (DSR)and Energy-Dispersive X-ray Spectroscopy (EDX). Further experiments of photocatalysis in aqueous solution of sulfide and sulfite for hydrogen evolution, were conducted. The samples were irradiated by monochromatic blue light, generated by an LED. From these experiments it was concluded that the presence of sulfate and acetate anions in the system results in more performantphotocatalysts than the presence of nitrate and especially chlorideanions

Non-ambient FTIR study of thermally treated seashells

A large quantity of waste seashells (millions of tons) is discarded annually after mollusc consumption, which becomes a problem for the environment worldwide as these shells are a habitat for microbes which could turn into a public health issue [1]. On the other hand, waste shell biomaterials need a small amount of energy for recycling and processing into useful products for various applications. Calcium carbonate is essential in biomineralization, where it is the primary constituent of mollusc shells, crustacean cuticles, corals etc. In its pure form, it occurs naturally, under normal temperature and pressure conditions, in three anhydrous crystalline forms, namely calcite, aragonite and vaterite [2]. At high pressures, two further forms, namely calcite II and calcite III, are formed. The most stable form of calcium carbonate at atmospheric pressure and room temperature is calcite. The presence of both calcite and aragonite is very frequent in biologically produced calcium carbonate minerals. Though aragonite is metastable in aqueous solution, it can nucleate [3]. Aragonite is found in the nacre of the shells of bivalve molluscs, which provide a protection for these animals [4]. From the study of the marine bivalve species Mercenaria mercenaria and Crassostrea gigas, Weiner et al. [5] have shown that amorphous calcium carbonate is a precursor phase of aragonite. The present study, which is part of our efforts to convert seashells into useful products like hydroxyapatite, investigates the temperature influence on the calcite and aragonite in a processed shell sample by using Fourier-transform infrared spectroscopy (FTIR)

Incubation-based hydroxyapatite synthesis method using shells as Ca2+ source

Hydroxyapatite, the well-known calcium phosphate, was obtained on the surface of shells fragments by partial conversion of the latter, which served both as template and also provided the calcium ions required for synthesis. Confirmation of hydroxyapatite formation was acquired by recording and analyzing X-ray diffraction patterns. The degree to which the phosphate ions were consumed during the incubation-based synthesis was determined using a phosphate minicolorimeter, and the results indicate that a nucleation process takes place in the first 4 hours

Influence of nucleation centers upon solvothermal growth of silver nano/microcrystals

Silver nano/microcrystals were obtained at medium pressure in a microwave field by using the solvothermal synthesis. In order to evaluate the nucleation centers’ influence upon the formed crystals’ morphology, investigations were conducted using scaffolds to stimulate their heterogeneous nucleation. Therefore, besides the silver and chloride nanocrystals used as nucleation centers, SiOx type spheres were used. The results indicate that the presence of the heterogeneous nucleation centers on the SiOx scaffolds plays a crucial role in the silver nano/microcrystals morphology