Introduction Graphite carbon nitride (g-C3N4) composite manganese cobalt based prussian blue (MnCoPBA/g-C3N4) catalyst was prepared by a self-assembly method, a coprecipitation method and a high-temperature annealing method. The catalyst prepared was used to analyze the catalytic degradation of rhodamine B (RhB) in the SR Photo Fenton like system. The MnCoPBA/g-C3N4 catalyst has a degradation efficiency of 96% for RhB within 10 minutes and exhibits a good cyclic stability. The catalyst also has a good catalytic degradation performance for RhB at pH values of 1-9, indicating a superior applicability in acidic, neutral, and weakly alkaline environments. Methods Catalytic performance test is an important indicator for evaluating MnCoPBA/g-C3N4 catalysts. A certain amount of MnCoPBA/g-C3N4 (0.05-0.20 g/L) catalyst was added into 100 mL of RhB (5-20 mg/L) solution. The suspension was stirred magnetically for 30 min to achieve adsorption-desorption equilibrium. Subsequently, 3 mL of suspension was taken and centrifuged to add the supernatant to a colorimetric dish. The data were recorded using a UV spectrophotometer. Subsequently, in a xenon lamp (350 W, >420 nm), a certain amount of PMS (5-60 mg/L) was added and 3 mL of suspension was treated by centrifugal force every 5 minutes to obtain the supernatant. The data were recorded in a UV spectrophotometer until the solution become colorless and the UV absorption spectrum data unchanged. The cyclic stability of catalysts is an important indicator for evaluating their practical application. To reduce the possible experimental errors caused by catalyst loss in the cyclic experiment, the cyclic experiment was designed as a parallel experiment, where each cyclic experiment was conducted independently. Sampling was no longer conducted during the n-1st cycle before the n-th cycle experiment, and sampling was conducted again during the n-th cycle experiment. The experimental operation was the same as the catalytic experiment. The waste liquid was collected and centrifuged, and the product was washed and dried with deionized water and ethanol. The UV spectrophotometer was used to test the data and collect records. Results and discussion Based on the analysis of the results, a possible catalytic degradation mechanism for the Photo-Fenton like system was proposed. The photocatalytic excitation of g-C3N4 semiconductor material in the Photo-Fenton like system generates photo- generated electrons and hole pairs, which are captured by metal ions in MnCoPBA and undergo a reduction reaction, achieving an effective separation of photo-generated carriers in the photocatalytic system and overcoming the defect of high photo-generated carrier recombination efficiency in g-C3N4 photocatalytic system. Simultaneously achieving a closed loop cycle of Fe(III)/Fe(II), Mn(III)/Mn(II) and Co(III)/Co(II) ions in the Fenton like system is obtained. An energy support for the Fenton like system is provided. The rate limiting step is broken through, and the defect of ion deficiency in the Fenton like system is overcome. Also, photo-generated electrons can directly activate PMS to generate SO4·-, triggering chain reactions to produce ·OH, and reacting with O2 to form ·O2-. Various strong oxidizing radicals efficiently degrade RhB, thus improving the catalytic degradation performance. Conclusions MnCoPBA/g-C3N4 catalyst was prepared by a coprecipitation method combined with a high-temperature calcination method. The effect of catalytic condition on the catalytic degradation performance of RhB was investigated. The results indicated that when MnCoPBA/g-C3N4-2.5 had the optimal catalytic degradation efficiency for RhB under the optimum condition (i.e., the catalyst dosage of 0.1 g/L, RhB concentration of 10 mg/L, PMS dosage of 0.15 g/L, and pH values of 1-9). The catalytic degradation mechanism indicated that Mn and Co metal ions in MnCoPBA acted as mediators for photocatalytic and the Fenton like connections, capturing photo-generated electrons to slow down the rate of photo generated electron hole recombination. Also, the reduced metal ions could promote the Fenton like reaction to decompose PMS, producing the more intense oxidizing free radicals and accelerating the catalytic degradation of RhB. The catalytic degradation efficiency of RhB was 90% within 2 min, and 96% within 10 min. In addition, the catalyst also exhibited a good cycling stability.