Sono-assisted Adsorption of As(V) from Water by Rice-Husk-Ash-Derived Iron-Modified Mesoporous Zeolite Y: A Cradle-to-Cradle Solution to a Problematic Solid Waste Material

Synergistic sono-adsorption and adsorption-enhanced sonochemical degradation of dyes in water by additive manufactured PVDF-based materials

The present study proposes the first mechanistic model accounting for the most meaningful physico-chemical phenomena taking place in liquid phase adsorption processes under ultrasound. Initially, this study was aimed at developing an easy-to-make and easy-to-recover piezocatalyst for the degradation of RhB in water by combining the high piezocatalytical performance of BaTiO3 with a compatible piezoelectric support such as PVDF, manufactured by a customised additive manufacturing - direct ink writing system with in-situ poling. However, initial results showed that the resulting PVDF-BaTiO3 composite slabs performed worse than BaTiO3 piezocatalysts on their own, and that poling did not have any effect on their performance (82% RhB removal after 2 h when using either poled or unpoled PVDF-BaTiO3 composite slabs compared to 92% RhB removal after 2 h in presence of BaTiO3 piezocatalysts). Further investigation with pure PVDF materials demonstrated that, instead of piezocatalysis, synergistic ultrasound-assisted adsorption and sonochemical degradation were taking place, enabling the removal of >95% of the dye within 40 min of ultrasound treatment in the presence of 4 g L-1 of additive manufactured PVDF slabs. The results of this study and their evaluation with the mechanistic model proposed for liquid phase adsorption under ultrasound suggest that the adsorption of RhB on additive manufactured PVDF slabs was enhanced by the structure, higher specific surface ratio and higher volume of mesopores achieved through the 3D-printing process, as well as the minimisation of film resistance to mass transport due to ultrasound. Moreover, adsorption on additive manufactured PVDF enhanced the sonochemical degradation of the dye due to its high concentration in the adsorbed phase. This study demonstrates that adsorption processes, especially in the presence of PVDF materials, may be significantly more important in piezocatalysis than what has been reported to date, to the point that the synergistic combination of sono-adsorption and sonochemical degradation in presence of additive-manufactured PVDF slabs may be enough to achieve high removal rates of dyes in water.

Synthesis and characterisation of transition metal sulphide-loaded fly ash-based mesoporous EU-12 photocatalysts for degradation of rhodamine B

Transition metal sulphide-loaded fly ash-based EU-12 photocatalysts were synthesized by sono-hydrothermal method followed by ion exchange. The composites were characterized by XRD, FESEM, DSC-TGA, Raman spectroscopy, and BET surface area analysis. The XRD results imply 76.39% crystallinity of EU-12 and morphological studies by FESEM, and TEM revealed the shape and size of EU-12, i.e. rod-shaped with size ranging from 5 to 200 nm. Band gap of all synthesized photocatalysts were found to be ≤ 3.44 eV. The photoactivities of the photocatalysts were examined by degrading rhodamine B (RhB). The results indicated that metal sulphide/EU-12 composite had the strong photoactivity under visible light compared to dark environment. Furthermore, the efficiency of photocatalysts was determined in terms of degradation efficiency towards RhB which was found to be maximum of 98.62% for 0.2 M CdS/EU-12 at 2 gL^-1 of catalyst dosage and 10 ppm of dye concentration within 3 h under visible light source of 200 W.

Simultaneous Methylene Blue Adsorption and pH Neutralization of Contaminated Water by Rice Husk Ash

In this study, the potential of rice husk ash (RHA) to act as an adsorbent for treating dye-containing wastewater was demonstrated. The RHA used in this study contained 91.7% silica, which was composed of crystalline (cristobalite and tridymite) and amorphous phases. The mechanochemical treatment of RHA led to an increase in its specific surface area from 6.2 to 14.6 m²/g in 15 min and dramatically improved its methylene blue (MB) adsorption ability. Langmuir adsorption isotherms revealed that the maximum adsorption capacity of the treated RHA was 8.59 mg/g, which is 2.45 times higher than that of raw RHA. pH-dependent adsorption studies on the RHA revealed that MB was adsorbed on the deprotonated Q³ silanol through electrostatic interactions. Moreover, the RHA adsorbent showed pH buffering at a pH value of approximately 7; thus, the pH of the solution could be neutralized simultaneously with the adsorptive removal of MB.