It has been shown that post-synthetic heat treatment of g-C3N4 in the melt of potassium and lithium salts leads to a significant increase of photocatalytic activity in the hydrogen formation from aqueous solutions of electron-donor compounds compared to the initial g-C3N4. This could be explained in terms of formation more crystalline graphitic carbon nitride (CGCN) with enhanced ability for absorption of higher amounts of visible light. Simultaneously, this treatment significantly decreases level of electron-hole recombination. It has been established that coincident use of two donors of different nature (organic acid and alcohol) with CGCN significantly increases rate of hydrogen formation. The possible explanation to this phenomenon could be find within acidic activation of CGCN. The influence of a number of factors on the efficiency of photocatalytic hydrogen production under visible light in systems based on the received carbon nitride has been investigated. The apparent quantum yields of the hydrogen evolution process with use of CGCN were determined as 23.6 and 5.6% at 405 and 435 nm, respectively.