Mesoporous, phase-pure Al3+ engrafted spinel ZnAlxB2−xO4 x = 0, 1; B = Cr3+/Fe3+) for effective fluoride chemisorption and photodegradation of azo/non-azo dyes

Abstract

Well-crystalline, cubic, spinel-type, mesoporous ZnAlxB2−xO4 [x = 0, 1; B= Cr3+ (abbreviated as ZAC0, ZAC1) and B = Fe3+ (abbreviated as ZAF0, ZAF1)] calcined at 700 °C for 3 h was synthesized by the solution-combustion method using urea and triethanolamine as precursors. The phase formation was confirmed by PXRD, TEM, and HRTEM analyses. The phase formation mechanism was established by simultaneously recorded TGA-FTIR hyphenation analyses. ZAC1 with SBET = 30.02 g/m2 and average pore size 5.67 nm, showed the highest ∼86.36 % of photodegradation efficiency for reactive black 5 and 98.00±2 % fluoride removal, and reusable up to 5th cycles at pH 7. The mechanisms of fluoride chemisorption and photodegradation were established by the surface-electrostatically-controlled-pH model. The chemisorption of fluoride was supported by XPS and FTIR analyses. The photodegradation followed the Pirkanniemi path as established by the HPLC, FTIR, and EPR studies, and Krӧger-Vink notation. Treatment of fluoride-containing field water sample analyses using ZAC1 was satisfactory.