The adsorption of dye molecules is an important process for the photodegradation removal of dye pollutants. In this work, a semiconductor photocatalyst of Cr-doped ZnO nanorods (Cr-ZnO NRs) was synthesized, and its adsorption-photocatalysis synergy (APS) effect was investigated for anionic methyl orange (MO-) and cationic methylene blue (MB+). The detailed thermodynamic information (including adsorption maximum capacity q(max), adsorption equilibrium constant K-ads and adsorption efficiency AE %) and dynamic information (including adsorption rate constant k(a), degradation rate constant k(d) and degradation efficiency DE %) were obtained to evaluate the different reaction performances for MO- and MB+. With q(max(MB+)) = 40.59 mg g(-1) > q(max(MO-)) = 15.95 mg g(-1), k(a(MB+)) = 20.61 min(-1) > k(a(MO-)) = 4.62 min(-1), and AE((MO-)) = 40% > AE((MO-)) = 9%, Cr-ZnO NRs showed much superior adsorption performance for MB+ than MO-. With k(d(MB+)) = 0.0430 min(-1) > k(d(MO-)) = 0.0014 min(-1) and DE(MB+) = 98% > AE((MO-)) = 20%, Cr-ZnO NRs also showed much superior photodegradation performance for MB+ than MO-. The APS mechanism of Cr-ZnO NRs is revealed to be multiple pi-pi interactions and stronger electrostatic attractions dominant for enhanced adsorption of MB+ and higher AE and more photocatalytic active species dominant for enhanced photodegradation of MB+. The APS was furthermore characterized and verified by zeta potential analysis, Fourier transform infrared investigation, and fluorescence imaging. The results indicate that Cr-ZnO NRs are promising adsorbent and photocatalyst candidates favorable for positive MB+ than negative MO-. Such an APS investigation can effectively help to improve the photodegradation treatment performance of photocatalysts for dye pollutant removal.