A MoS2/g-C3N4 composite was synthesized by a significantly simple method using Na2MoO4 and thiourea as precursors, without the need for a hydrothermal or an ultrasound step. The photocatalytic activity of the synthesized material was evaluated by the degradation of rhodamine B (RhB) in aqueous solution under blue light. The composites with low content of MoS2 performed better than pure g-C3N4. Using a low-power light-emitting diode light source, an improvement of two orders of magnitude in the photochemical space-time yield was achieved, proving enhanced energy efficiency and productivity compared to earlier studies. The degradation pathway of organic pollutants was confirmed by the effects of selective scavengers.