An excellent metal-free photothermal catalyst, phosphorus and nitrogen co-doped carbon (PNC) with micro/mesoporous structure, was fabricated by annealing sustainable cellulose and ammonium phosphate dibasic ((NH4)2HPO4) in inert atmosphere. (NH4)2HPO4 not only provides phosphorus and nitrogen sources but also creates micro- and mesopores (with a high surface area of 543.7 m2/g) in carbon material during carbonization of cellulose. The carbon material PNC exhibits high catalytic activity for the hydrogenation of nitroarenes with hydrazine hydrate under the irradiation of Xenon lamp. Experimental results prove that light irradiation and its thermal effect were essential to the catalytic performance, which indicated that this is a photothermal catalytic process. Control experiments and characterizations illustrate that PNC has relative smaller electronic resistance and P/N dopants were key factors to its catalytic performance. First-principles computations have also demonstrated that the P/N dopants could regulate the charge distributions so that an impurity energy level near fermi level is generated PNC catalyst. Therefore, the electron-hole pair and charge transfer are easily driven by irradiation in the PNC catalyzed system, which gives a good explanation for the unique photothermal catalytic activity of PNC in the hydrogenation of nitroarenes.