The correlation of bandgap with the crystallite size using the quantum confinement effect for wastewater treatment

Abstract

Porous structured materials have immense applications in the refinement of wastewater. The metal oxides blended with 2-D porous materials can be used as an efficient photo-catalyst for the treatment of polluted water. For this purpose, we have synthesized water-stable Ni 0.3 Zn 0.7 Fe 2 O 4 (NZF) and Ni 0.3 Zn 0.7 Mg 0.05 Fe 1.95 O 4 (NZMF) and Ni 0.3 Zn 0.7 Mg 0.05 Fe 1.95 O 4 /r-GO (NZMF@rGO) porous materials for degradation of toxic contaminants from industrial waste. The prepared materials were characterized by XRD, SEM, and UV-Visible spectroscopy and further used as photo-catalytic entities for the degradation of crystal violet (CV) and benzoic acid (BA) as targeted pollutants. The optical band gap of NZMF (1.79 eV) was higher than pristine NZF (1.74 eV) and the reduction (NZF = 22.59 nm and NZMF = 22.45 nm) in the crystallite size according to the quantum confinement effect as the different ionic radius and electronic configuration of magnesium (Mg) compared to Fe are likely to alter the crystal and electronic band structures, thus influencing the bandgap and crystallite size. EIS analysis presented higher value of charge transfer by NZMF because of lower value of charge transfer resistance (Rct = 4.34 Ω) than the pristine NZF. The photocatalytic experiment presented the maximum degradation of targeted pollutants (BA= 72.05%, CV= 92.6%) using rGO comprised NZMF. Hence, NZMF@rGO can be used as an interesting photoactive material for the conversion of poisonous chemicals into functional by-products (H 2 O and CO 2 ). • Pristine Ni 0.3 Zn 0.7 Fe 2 O 4 (NZF), Ni 0.3 Zn 0.7 Mg 0.05 Fe 1.95 O 4 (NZMF) and Ni 0.3 Zn 0.7 Mg 0.05 Fe 1.95 O 4 @r-GO (NZMF@rGO) are fabricated via sol-gel and ultrasonication method. • The smaller crystallite size and higher bandgap energy for NZMF are correlated by the quantum confinement effect. • Visible light active photo-catalysis of fabricated samples was done against crystal violet and benzoic acid pollutants. • The maximum degradation is observed by NZMF@rGO in just 35 minutes under Xenon source.