Search results for "Gradation"

Ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by a thermoresistometer

2004

Abstract The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with E a =46.36 kJ/mol for aerobic degradation and E a =49.57 kJ/mol for anaerobic degradation.

ChemInform Abstract: Coupled Semiconductor Systems for Photocatalysis. Preparation and Characterization of Polycrystalline Mixed WO3/WS2 Powders.

2010

Mixed WO3/WS2 powders were prepared by oxidation of WS2. The physical properties of the samples were characterized by X-ray diffraction, diffuse reflectance spectroscopy, and scanning electron microscopy; they were strongly dependent upon the time and temperature of oxidation. The chemical state and the elemental distribution of the sample surface were investigated by X-ray photoelectron spectroscopy. The photocatalytic results have showed that the aqueous suspensions of the mixed WO3/WS2 systems have significantly higher activities than pure WS2 and WO3 for the photodegradation of phenol. The enhanced performance can be related to the presence of heterojunctions WO3/WS2 on the single parti…

FI-chemiluminometric study of thiazides by on-line photochemical reaction

2004

The present manuscript deals with a simple and sensitive flow-injection method for the chemiluminescent determination of thiazides. The method is based on the on-line photodegradation and chemiluminescent determination of the resulting photo-fragments. The on-line photodegradation is performed in basic medium by using a photoreactor consisting of a 550 cm long x 0.8 mm ID piece of PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. The determination of the photo-irradiated thiazides is performed by a chemiluminescent oxidative reaction with Ce(IV) in sulphuric acid medium. A heterogeneous group of thiazides (indapamide, metolazone, hydroflumethiazide, chlorthalidone and be…

POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) AS BIOMARKERS FOR ASSESSING BIODEGRADATION SUSCEPTIBILITIES OF CRUDE OIL SPILLED ON SOILS

2008

<p><em>Kemudahan mengalami biodegradasi senyawa-senyawa polisiklik aromatik hidrokarbon (PAHs) dalam minyak mentah yang diekstrak dari tanah pada hari ke-0 dan ke-39 telah ditentukan. Sampel tanah yang digunakan dikontaminasikan dengan minyak mentah Barrow sebanyak 5% (w/w) untuk memperoleh sampel tanah yang sama dengan kondisi lingkungannya. Tingkat biodegradasi dari minyak mentah Barrow yang diekstrak dari sampel tanah pada hari ke 0 dan hari ke 39 ditentukan berdasarkan fraksi senyawa PAH yang dianalisis menggunakan GC-MS. Persen perubahan kelimpahan (abundances) terhadap waktu dari beberapa senyawa alkilnaptalena ditentukan untuk mengetahui urutan kemudahan terdegradasinya i…

Porous materials as delivery and protective agents for Vitamin A

2016

The suitability of porous materials to immobilize and release under control bioactive molecules prompted us to design and study delivery systems of Vitamin A (VitA). This molecule, relevant in several physiological functions, is easily oxidized. Commercial VitA was immobilized in two different clays, montmorillonite K-10 (MMT) and sepiolite (SEP), and in MCM-41, by impregnation. Characterization of the resulting hybrid materials by XRD, FTIR and 13C and 29Si (MAS) NMR spectroscopies revealed its presence. The photo-stability tests showed decreased degradation of VitA in the clays, compared to MCM-41 and the pure VitA, while thermostability is observed until ∼100 °C. The kinetics of the rele…

The expanding role of LC-MS in analyzing metabolites and degradation products of food contaminants

2008

Abstract Liquid chromatography-mass spectrometry (LC-MS) has contributed significantly in advancing research in the analysis of metabolites and degradation products of food contaminants. Of particular interest is the comprehensive application of LC-MS to discovery of degradation products and metabolites. This review, covering research published between 2003 and 2008, describes how LC-MS has been used in this field, with the majority of work dealing with target-metabolite analysis and only a small fraction using LC-MS comprehensively. In considering the significance of this topic and the potential interest in it, we briefly describe state-of-the art mass analyzers applied for it (QtrAP, QqTO…

1984

Surface characterisation of metal ions loaded TiO2 photocatalysts: structure–activity relationship

2004

Abstract Transition metal loaded TiO 2 powders were characterised and tested for the photodegradation of some organic acids. Both Lewis and Bronsted surface acid sites were present in the samples containing large amounts of Mo, V and W. The Bronsted sites are associated to the presence of the transition metals as they do not exist in the unloaded support, and in particular to the presence of these metals in high oxidation states. The trend of the pzc values of the various powders matches rather well both with the surface acidity of the samples experimentally determined by NH 3 adsorption and with a scale of acidity/basicity for bulk binary oxides. XPS investigation indicates that only the p…

Preparation and photoactivity of nanocrystalline TiO2 powders obtained by thermohydrolysis of TiOSO4

2013

Nanocrystalline TiO2 photocatalysts were synthesized in mild conditions by thermohydrolysis of TiOSO4 in water at 100 °C and post-calcination treatment at various temperatures. The TiO2 powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area determinations, scanning electron microscopy and electron paramagnetic resonance measurements. The photoactivity of the samples was tested employing the photodegradation of 4-nitrophenol in liquid–solid regimen and the photooxidation of gaseous 2-propanol. The best results were obtained with the powder calcined at 600 °C for 10 h. Surprisingly, the not calcined sample was the most active for the abatement…

Analyzing Regional Geographic Challenges: The Resilience of Chinese Vineyards to Land Degradation Using a Societal and Biophysical Approach

2021

Land degradation, especially soil erosion, is a societal issue that affects vineyards worldwide, but there are no current investigations that inform specifically about soil erosion rates in Chinese vineyards. In this review, we analyze this problem and the need to avoid irreversible damage to soil and their use from a regional point of view. Information about soil erosion in vineyards has often failed to reach farmers, and we can affirm that to this time, soil erosion in Chinese vineyards has been more of a scientific hypothesis than an agronomic or environmental concern. Two hypotheses can be presented to justify this review: (i) there are no official and scientific investigations on viney…