Noble metal-free zinc oxysulfide (Zn(O,S)) nanoparticles for H-2 evolution had been facilely synthesized by a low-cost chemical reaction at low process temperature of 70-90 degrees C with zinc acetate dihydrate as the zinc source and different amounts of thioacetamide as the sulfur precursor. The as-prepared Zn(O,S) had a nano crystallite size of 3-10 nm and formed aggregates. Low temperature process has led to the difficulty in forming well crystalline nanoparticles, therefore the ionic bonding is weaker as compared to the high temperature one. Due to the entropy-controlled reaction, Zn(O,S) with different compositions, phases, and bandgaps was formed and proposed to have a three-dimensional multibandgap-quantum-well (3D MQW) band structure, as supported by the selected area electron diffraction of high resolution transmission electron microscopy. Photo reduction of Cr6+ was initially performed for our materials selection. The photocatalytic hydrogen evolution reaction (HER) of Zn(O,S) in different kinds of solutions under low power UV lamps (the intensity is 0.088 mW/cm(2) or approximately 1/40 times UV light intensity of sunlight) was executed. A high efficient hydrogen evolution rate of 213 mu mol/g h watt was achieved by considering the input light power. The active surface oxygen anion-involved photocatalytic mechanism for HER is proposed, which was derived from the reversible change in Zn(O,S) color and the results from HER reactions in different solutions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.