NiO-TiO2 (TN) nanocomposite is synthesized from an assembly of p-type nickel oxide (NiO) and n-type titanium oxide (TiO2) in an ultrasound assisted operation. Transmission electron microscopy (TEM) demonstrates the existence of hexagonal particles in the nanocomposite. Dynamic light scattering (DLS) measurements show stable TN nanoparticles (NPs) at a negative zeta potential (-18.5 +/- 0.8 mV). The nanocomposite is tested for its catalytic activity towards degrading malachite green (MG), a known water toxicant and methylene blue (MB) under ultraviolet (UV) irradiation. Response surface methodology (RSM) is employed to optimise the influence of significant variables such as initial dye concentration, catalyst dose and time. Their mutual interactions are mapped by response surface and contour plots and correlated with degradation process by a designed model. The best photocatalytic efficiency (87%) is observed at an optimised concentration of 5 ppm dye with 10 ppm catalyst. The presence of inorganic ions and organic matter hardly affected the aggregate size of TN but caused a decline in photoactivity. The catalyst is found effective even in real water system (Hooghly River). A (Fluorine doped tin oxide) FTO/TN/Al heterojunction is fabricated. TN showed enhanced carrier mobility (1.03.10(-4) m(2)V(-1)s(-1)) and low transit time (1.76.10(-)(6) s) evaluated using space charge limited current (SCLC) theory. The nanocomposite appears suitable for energy preservation and environmental applications. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.