Reagent

About: Reagent is a research topic. Over the lifetime, 60091 publications have been published within this topic receiving 1234928 citations. The topic is also known as: reagens.

Time-Resolved In-Situ Energy and Angular Dispersive X-ray Diffraction Studies of the Formation of the Microporous Gallophosphate ULM-5 under Hydrothermal Conditions

Abstract: The hydrothermal synthesis of the large-pore oxy-fluorinated gallophosphate ULM-5 has been followed in situ using time-resolved energy dispersive and angular dispersive X-ray diffraction. A variety of synthetic parameters such as temperature, reagent stoichiometry, source materials, and pH have been studied, and their effect on the crystallization determined. The nature of the phosphorus source used, either orthophosphoric acid or phosphorus pentoxide, is found to have a profound influence on the reaction pathway. Using orthophosphoric acid, ULM-5 is found to form very rapidly following a short induction period. A kinetic analysis of the crystallization of ULM-5 using orthophosphoric acid under isothermal hydrothermal conditions has been performed. Comparison of the experimentally determined extent of reaction (R) versus time data with those predicted by various theoretical models indicates that over a wide range of temperatures and pH the crystallization can be modeled by a three-dimensional diffusion-controlled process. This process occurs at a rate essentially independent of temperature and pH. In contrast, using phosphorus pentoxide, the formation of ULM-5 is found to proceed via the formation of either of two distinct crystalline intermediate phases, which subsequently react to form the ULM-5 final product at a rate which is strongly dependent on temperature. The relative quantities of each intermediate phase formed depend critically on the precise reagent stoichiometry used. Conditions have been identified in which ULM-5 can be formed exclusively via either intermediate phase. The mechanism of transformation of intermediate to product phases appears to be either a direct solid- solid transformation, or via the dissolution or amorphorization of only a small quantity of material at the surface of the intermediate crystallites.

Use of iron minerals in optimizing the peroxide treatment of contaminated soils

Abstract: The treatment of silica sand contaminated with pentachlorophenol (PCP) using the standard Fenton's reagent procedure, sequential addition of iron (II) and H 2 O 2 , and a goethite (α-FeOOH)-H 2 O 2 system was investigated. The standard Fenton's procedure oxidized 10 mg/L soluble PCP, but was ineffective in degrading 10 mg/kg or 250 mg/kg particulate and sorbed PCP in silica sand. Sequential addition of excess reagents (480 mg/L iron (II) and 7% H 2 O 2 ) degraded particulate and sorbed PCP, but with high stoichiometric H 2 O 2 requirements. The most efficient system for PCP degradation was the H 2 O 2 -goethite system