Optimization of photocatalytic degradation of rhodamine B using Box-Behnken experimental design: Mineralization and mechanism.

The aim of this work was to optimize the photocatalytic degradation of rhodamine B (RhB) using a four-factor Box-Behnken experimental design, and the study was carried out under artificial irradiation (24-W UV lamp) using ZnO in suspension. The Box-Behnken model has been validated with an error less than 5%. A total (100%) RhB removal and COD abatement rates were reached under optimal conditions of treatment time, ZnO dose, and stirring speed at different concentrations of dye. The study of the effect of irradiation type (solar and UV lamp) on the degradation of RhB showed that solar irradiation gave a better rate of degradation with complete discoloration after 2 hr. The study of RhB degradation mechanism indicates that O 2 ∙ - were the main active species for the degradation of this pollutant. The comparison between the degradation of RhB alone and RhB prepared with varnish (as it is usually used in industry) revealed that degradation of RhB alone is faster comparing than that of RhB/varnish mixture. The results showed that the biodegradability was improved after a contact time of 60 min with a BOD5 /COD ratio increasing from 0.23 to 0.90. PRACTITIONER POINTS: Optimization of the photocatalytic degradation of rhodamine B using a four-factor Box-Behnken experimental design. Investigation of dye mineralization. The degradation mechanism of rhodamine. Biodegradability assessment based on the BOD5 /COD ratio.

Nickel removal by biosorption onto medlar male flowers coupled with photocatalysis on the spinel ZnMn2O4.

Ni2+ is a highly toxic above 0.07 mg/L and its removal is of high significance. The biosorption of Ni2+ onto medlar male flowers (MMF) was studied in relation with the physical parameters like pH, contact time, biosorbent dosage, Ni2+ concentration and temperature. The interaction biosorbent-Ni2+ was examined by the FTIR technique. The equilibrium was achieved within 40 min and the data were well fitted by the Langmuir and Redlich-Peterson (R-P) models. The maximum Ni2+ uptake capacity was 17.073 mg/g at 25°C and the Ni2+ removal follows a pseudo-second order kinetic with activation energy of 13.3 kJ/mol. The thermodynamic parameters: ΔS°, ΔH° and ΔG° showed that the biosorption was spontaneous and endothermic. MMF was used as a post treatment technique and the biosorption was coupled with the visible light driven Ni2+ reduction over the spinel ZnMn2O4. The effect of the pH, ZnMn2O4 loading and light intensity on the photoactivity was investigated. 77.5% of Ni2+ was reduced after ~140 min under optimal conditions. The Ni2+ removal reached a rate conversion of 96% of with the coupled system biosorption/photocatalysis is very promising for the water treatment.