## 1 Introduction  
Refractory organic contaminants in industrial wastewater are often intractable to the traditional wastewater system and harmful to the environment, thus their treatment technologies have attracted extensive attention worldwide. Fenton reaction is viewed as a useful and feasible method to remove these pollutants [1]. It involves the transformation of H\({}_{2}\)O\({}_{2}\) into strongly oxidized hydroxyl radicals (\(\bullet\)OH) under the catalyzation of Fe\({}^{2+}\), which could subsequently promote radical chain reactions leading to the degradation of refractory organic compounds [2]. However, the application of Fenton reactions was limited to strict acidic conditions, and plentiful iron sludge would be formed during the reactions [3]. On the other hand, the cost of H\({}_{2}\)O\({}_{2}\) is also one of the major stumbling blocks in its application. It seems that the heterogeneous Fenton-like technology with low H\({}_{2}\)O\({}_{2}\) consumption could overcome these shortcomings and significantly improve the ability of water treatment [4]. As a green and efficient oxidant, the demand for hydrogen peroxide in many fields is increasing year by year [5; 6; 7]. H\({}_{2}\)O\({}_{2}\) has active chemical properties and is difficult to preserve and transport. In a typical Fenton reaction, the addition amount of H\({}_{2}\)O\({}_{2}\) should far exceed the stoichiometric ratio. That is, much H\({}_{2}\)O\({}_{2}\) added was consumed ineffectively in reactions. For example, [PERSON] et al. [8] calculated that 25.4% of added H\({}_{2}\)O\({}_{2}\) was utilized for organic degradation in a homogeneous system, while the efficiency is only 0.4% in a heterogeneous Fe\({}_{3}\)O\({}_{4}\)/H\({}_{2}\)O\({}_{2}\) system. Excess H\({}_{2}\)O\({}_{2}\) is prone to decompose to O\({}_{2}\) on the catalyst surface. From this point of view, the slowly in situ generation of H\({}_{2}\)O\({}_{2}\) and its direct transformation into ROS is a feasible method to prevent the waste of H\({}_{2}\)O\({}_{2}\). The direct synthesis of hydrogen peroxide using hydrogen and oxygen as raw materials and noble metal as catalysts has attracted much attention [9,10]. In the field of wastewater treatment, it seems that formic acid is one of the most promising hydrogen carrier materials. Although the hydrogen content in formic acid is only 4.4 wt%, the hydrogen production performance is superior to that of most other hydrogen-containing materials in terms of simplicity, availability to net capacity ratio, and experimental environment [11,12]. More importantly, formic acid is biodegradable, and its acidity averts extra pH adjustment for Fenton-like reactions. It is particularly suitable for the pretreatment of industrial wastewater, which contains lots of refractory organic contaminants. Previous studies have reported the Pd-based catalysts for the successful generation of H\({}_{2}\)O\({}_{2}\) using formic acid [13]; however, when used in organic removals, pure oxygen and pH adjustment are still in need [13]. To further simplify the process and lower the cost, a more active catalyst that could facilitate the formic acid dehydrogenation and \(\bullet\)OH yielding is aimed to fabricate in this study. Graphitic carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) is a graphite-like material with stable chemical properties [14]. g-C\({}_{3}\)N\({}_{4}\) can be synthesized by simple pyrolysis through low-cost N-rich precursors such as melamine, ammonium thiocyanate, urea, and thiourea [15]. Its popularity originates from the ability as a non-metal catalyst for H\({}_{2}\) yielding through water splitting. Later studies reveal its versatile properties in several fields, for example, Fenton-like reactions [16]. Basically, g-C\({}_{3}\)N\({}_{4}\) could accelerate the catalytic ability in two ways: one is the anchor of metal atoms and the other is to increase the electron conduction rate as a transport carrier [17,18].