Plasma-modified wood sawdust waste for the removal of reactive blue II anionic dye from aqueous solution

The Removal of an anionic Reactive Blue 2 (RB2) dye in an aqueous solution was successfully achieved using a plasma-modified agricultural biomaterial waste. Sawdust from Moabi (Baillonellatoxisperma) and Sapelli (Entandrophragmacylindricum) was modified using non-thermal gliding arc plasma. The natural raw materials and plasma treated were characterized by Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), XRD, Chemical analysis by Fluorescence, Sorption Analyser, and Zetametry. Experimental parameters such as initial pH, contact time, adsorbent dose, initial RB2 concentration, and temperature were optimized. The results showed that the removal of Reactive Blue 2 dye was favorable at acidic pH conditions with the maximum capacity going from 172,85 to 200,91 mg.g-1 to 98,19 and 149,02 mg.g-1  respectively for raw and plasma-treated Sapeli and Moabi. The Avrami fractional-order kinetic provided the best fit to the experiments data and the thermodynamic adsorption data of untreated (SSB and SMB) and plasma-treated (SSM and SMM) sawdust followed an exothermic process. This work demonstrated that non-thermal plasma modified wood sawdust can be a good alternative absorbent for the removal of dye pollutants from an aqueous solution

Contribution a l\'Etude de la Structure Cristallographique et a la Synthese de l\'Indium (III) Meta Trithio-Antimoniate In(α-Sbs3)

Résumé Au cours de la tentative de synthèse de [In(SbS2) 2] 2 homologue de [In(PS2) 2] 2 suivant la même technique précédemment décrite, un gradient de température dans un four tubulaire nous a fait obtenir plutôt un produit cristallisé qui s\'est révélé être l\'indium (III) méta trithio-antimoniate [In(α-SbS3)]. Ce composé est obtenu pur seulement en ampoule de quartz scellé sous vide (10-6 mm Hg), soit dans les mélanges équimolaires soit d\'antimoine et d\'indium en présence d\'un excès de soufre, soit les deux sulfures dont le chauffage à 800 °c est suivi d\'un refroidissement lent dans le four jusqu\'à la température ambiante. Le composé [In(α-SbS3)] est iso structural de [In(α-SbSe3)]. Une analyse par microsonde électronique a permis de confirmer la composition chimique de ce ternaire. Il cristallise dans le système orthorhombique (groupe d\'espace pnma) et ses paramètres de maille sont a = 9,300(3) Å, b = 3,816(1) Å, c = 13,348(4) Å, v = 473,7 Å3 et Z = 4. La structure a été affinée par la méthode de moindres carrés avec une précision R = 0,0025. Les atomes In et Sb ont été distingués sans ambiguïté par les résultats des calculs des moindres carrés et par la coordination dans la structure. (Af. J. of Science and Technology: 2003 4(1): 39-43

Élimination du Noir Eriochrome T par plasma glidarc

L’élimination d’une solution aqueuse de Noir Eriochrome T (NET), composé organique largement utilisé en industrie textile, a été effectuée par plasma glidarc. Ce procédé d’oxydation avancée (POA) met en jeu les espèces gazeuses actives créées dans la décharge, principalement les radicaux OH°, son dimère H2O2 et le peroxynitrite ONOO- (dérivé de l’oxyde nitrique). Ces espèces induisent des propriétés fortement oxydantes qui sont largement employées pour la destruction de déchets organiques. Outre les espèces oxydantes, certains composés issus du radical NO°(HONO et ONOOH) et présents en solution confèrent également au plasma des propriétés acidifiantes qui accélèrent ainsi les réactions d’oxydation. L’étude spectrophotométrique d’une solution de NET (15 µM) exposée à la décharge électrique a permis de révéler qu’aux premiers instants du traitement (t < 3 min), il se forme un composé intermédiaire qui absorbe à λ = 752 nm; la cinétique de décoloration observée présente une loi de variation d’ordre global égal à un avec une constante de vitesse k = 2,11 min‑1. Après 45 min de traitement, un taux de décoloration de 85,1 % est obtenu. Au bout du même temps, le composé présent initialement en solution à 15 µM se minéralise à 57,3 % avec une constante de vitesse k1 = 0,0188 min‑1. L’obtention d’un abattement de 67 % de la demande chimique en oxygène (DCO) avec une constante de vitesse k2 = 0,0253 min‑1 permet de confirmer que le composé se dégrade bien sous l’effet de la décharge. Par ailleurs, bien que la cinétique de disparition d’une solution plus concentrée (150 µM) soit plus lente (k3 = 0,0178 min‑1), le composé se décolore à 82,0 % et un taux de dégradation de 86,6 % est obtenu après une durée d’exposition de 50 min. Les analyses qualitatives effectuées juste après arrêt de la décharge ont également révélé la présence en solution des ions minéraux issus de la dégradation de la molécule.The elimination of an aqueous solution of Eriochrome Black T, an organic compound widely used in the textile industry, was carried out using a gliding arc plasma. This advanced oxidation process (AOP) involves the active gaseous species created in the discharge, mainly OH° radicals, its dimer H2O2, and peroxynitrite ONOO- (a nitric oxide derivative). These species induce highly oxidizing properties which are widely used for the destruction of organic wastes. In addition to the oxidizing species, some derivatives of the NO radical (HONO and ONOOH) present in solution also confer on the plasma some acidifying properties, which accelerate the oxidation reactions. The spectrophotometric study of an Eriochrome Black T solution exposed to an electric discharge showed that an intermediate compound which absorbs at 750 nm forms at the beginning of the treatment (t < 3 min) with a relevant pseudo first order kinetic rate constant k = 2.11 min‑1. After 45 min of treatment, a decolouration rate of 85.1% was obtained and the compound initially present in solution at a concentration of 15 μM was mineralized (57.3%) with a rate constant k1 = 0.0188 min‑1. The observation of a concurrent 67% decrease in chemical oxygen demand with a rate constant k2 = 0.0253 min‑1 confirms the degradation of the compound as a result of the discharge. Although the kinetics of disappearance of a more concentrated solution (150 µM) are slow (k3 = 0,0178 min‑1), the compound faded at 82.0% and a degradation of 86.6% was obtained for an exposure time of 50 min. Qualitative analysis performed immediately after the discharge also revealed the presence in solution of mineral ions derived from the degradation of the parent molecule

Air Quality and Human Health Risk Assessment in the Residential Areas at the Proximity of the Nkolfoulou Landfill in Yaoundé Metropolis, Cameroon

Landfill operations generate particulate matters (PM) and toxic gases that can jeopardize human health. This study was conducted in February 2016 to assess the air quality in the residential areas around the Nkolfoulou landfill in Yaoundé. The concentrations of PM2.5 and PM10 were determined with Dust Sentry while those of CO, O3, NO2, CH4, CO2, CH2O, H2S, and SO2 were measured using gas sensors. At the landfill neighborhood, 30% of the daily mean concentrations of PM2.5 and PM10 crossed the daily safe limits. The concentrations of CO, O3, NO2, SO2, and H2S recorded at the propinquity of the landfill complied with the emission standards. Near the landfill, hourly mean concentrations of CH2O and H2S higher than their odour thresholds were recorded at each sampling site. The concentrations of CH4 were less than its lower explosive limit while those of CO2 were far below the safe limit for occupational health. The values of cancer risk (CR) due to the inhalation of CH2O were >10−6 while those of hazard index (HI) due to the inhalation of CH2O, H2S, and SO2 were <1. Thus, there might be increased cancer risks at the Nkolfoulou landfill neighborhood, whereas the increased non-cancer risks were low. 96.76% of the daily average levels of air pollutants registered near the landfill surpassed those recorded at the remote control site. Hence, the landfill operations might be supplying air pollutants to the neighbouring residential areas

Temporal post-discharge reactions effect on the oxidative catalytic properties of plasma-synthesized α-MnO2 nanorods

The evolution of the morphology, crystalline structure, and textural properties of α-MnO2 nanorods, which were obtained after reduction of a KMnO4 solution via gliding arc plasma process, have been followed along their ageing under temporal post-discharge conditions. When aged at 25 °C a partial transformation of α-MnO2 (cryptomelane) to γ-MnO2 (nsutite) occurred with an increase of specific surface area from 98 to 141 m2/g. In parallel, the starting nanorods were converted to nanoneedles after 24 and 48 h, and into nanosheets after 72 h. These transformations are ascribed to the evolution of maturation process of crystallites, thanks to post-discharge species (H2O2, HOONO,…). At the opposite, ageing at 100 °C induced a remarkable transformation of α-MnO2 to γ-MnO2 with a decrease of specific surface area from 98 to 35 m2/g after 3 h, which was in line with the observed agglomeration of nanorods. Finally, whereas a longer ageing at 100 °C provoked an activity diminution of the material, an augmentation of activity of plasma-synthesized α-MnO2 was recorded when implementing ageing at 25 °C

Assessment of the Nutrients in the Leachate and the Groundwater Quality for Drinking and Farming around the Nkolfoulou Landfill in Yaoundé, Cameroon

This study focuses on the assessment of the nutrients in the leachate and the groundwater quality around the Nkolfoulou landfill in Yaoundé known in French as “Centre de Traitement de Déchets (CTD).” Landfilling generates leachate that can pollute groundwater. Leachate along with groundwater samples (n=1+13) was collected in January (long dry season) and May (long wet season) 2014 and explored for various parameters including pH, temperature, EC, turbidity, TDS, TA, TSS, TH, BOD5, COD, Na+, K+, Mg2+, Ca2+, NH4+, NO3−, Cl−, F−, SO42−, PO43−, HCO3−, and colour using standard methods. In the leachate samples, values of TSS (700.2 and 130.2 mg/L), BOD5 (140 mg/L), COD (1350 and 1750 mg/L), NH4+ (82.50 and 39.51 mg/L), NO3− (159.32 and 74.82 mg/L), and Cl− (702.69 and 345.50 mg/L) exceeded the Cameroonian standards for effluent discharge. All the values of pH and some values of turbidity (4.55 and 4.50 NTU) and NH4+ (0.51 and 0.73 mg/L) in the groundwater samples violated the Cameroonian standards for drinking water. Based on the water quality index (WQI), an average of 11.53% of groundwater samples was improper for drinking in both seasons. Based on the parameters assessed, all the samples complied with the standard set for irrigation, poultry, and livestock. The hazard quotient (HQ) and the hazard index (HI) of NO3− and F− for children and adults were <1, and hence, the increased non-cancer risks due to these ions through the drinking of groundwater was low. From the statistical analysis, the Nkolfoulou landfill may not be the main source of major ions to the nearby groundwater

Temporal post-discharge reactions effect on the oxidative catalytic properties of plasma-synthesized α-MnO2 nanorods

The evolution of the morphology, crystalline structure, and textural properties of α-MnO2 nanorods, which were obtained after reduction of a KMnO4 solution via gliding arc plasma process, have been followed along their ageing under temporal post-discharge conditions. When aged at 25°C a partial transformation of α-MnO2 (cryptomelane) to γ-MnO2 (nsutite) occurred with an increase of specific surface area from 98 to 141 m2/g. In parallel, the starting nanorods were converted to nanoneedles after 24 and 48 hours, and into nanosheets after 72 hours. These transformations are ascribed to the evolution of maturation process of crystallites, thanks to post-discharge species (H2O2, HOONO,…). At the opposite, ageing at 100°C induced a remarkable transformation of α-MnO2 to γ-MnO2 with a decrease of specific surface area from 98 to 35 m2/g after 3 hours, which was in line with the observed agglomeration of nanorods. Finally, whereas a longer ageing at 100°C provoked an activity diminution of the material, an augmentation of activity of plasma-synthesized α-MnO2 was recorded when implementing ageing at 25°C

Non-thermal plasma synthesis of sea-urchin like alpha-FeOOH for the catalytic oxidation of Orange II in aqueous solution

In this study, a template-free synthesis of iron oxyhydroxide nanostructures by gliding arc plasma at atmospheric pressure was evaluated. The results showed that exposure of a Mohr’s salt solution to the plasma discharge induces a rapid oxidation–precipitation of iron(II) into a non-porous and amorphous iron(III) (hydr) oxide. After ageing in temporal post-discharge for three hours, the amorphous iron (hydr) oxide was transformed into crystalline goethite (α-FeOOH). The presence of goethite was confirmed by FTIR, Raman spectroscopy and thermogravimetric analysis. Textural analyses showed that the material is mesoporous with a BET surface area of 134 m2 g−1. SEM pictures revealed that the plasma-synthesized goethite particles consist of sea-urchin like hollow spheres. The catalytic activity of such goethite in the Fenton degradation of Orange II (organic dye) showed that this material can be used as heterogeneous catalyst for effective removal of organic pollutants from wastewater. This study establishes that the plasma discharge of gliding arc type can be used as a green and cheap efficient route for the synthesis of porous metal oxide nanostructures

Thermal treatment of plasma-synthesized geothite improves Fenton-like degradation of orange II dye

Various iron oxides are used for Fenton reactions to degrade organic pollutants. The degradation efficiency may be improved by transforming an iron oxide phase to another. Here, we report on the transformation of goethite into hematite by thermal treatment at 400 °C. The products were analyzed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and N2-physisorption. The catalytic activities were measured for orange II bleaching at initial concentration of 25 mg L−1, pH 3, catalyst concentration of 0.2 g L−1; 5 mM H2O2, 30 °C. Results show that the synthesized goethite was successfully transformed into hematite, and the specific surface area of the material increased from 134 to 163 m2 g−1. The bleaching efficiency of the orange II dye reached 100 % for the hematite product, versus 78 % for goethite. Therefore, a moderate thermal treatment of a plasma-synthesized goethite improves the catalytic oxidation of organic pollutants

Surface modification of smecticte clay induced by non-thermal gliding arc plasma at atmospheric pressure

Smectite clay from Sabga (west-Cameroon) was treated in aqueous suspension by gliding arc plasma to modify its surface properties. The evolution of the modifications was followed with the exposure time and post-discharge duration using Fourier transformed infra red spectroscopy and scanning electron microscopy. X-ray diffraction and nitrogen physisorption analyses were also performed to evaluate if both crystalline and textural properties of the material are affected by the treatment. The results obtained show that the plasma treatment causes the breakdown of structural bounds at the clay surface and induces the formation of new hydroxyl groups (Si–OH and Al–OH) on the clay edges. Crystallinity, sheet structure and textural properties are not significantly affected by the plasma treatment. However, it should be noted that an intensive treatment of the clay lowers the pH of the suspension, which subsequently induces an acid attack of the clay. In such case, the specific surface area of the clay increases. This study demonstrates that gliding arc plasma treatments can be used to activate clay minerals for environmental application