Microwave-synthesized SnO2 (SnO2-M) with smaller size, larger surface area, and abundant oxygen vacancies was confirmed by experiments and DFT to promote charge separation and CIP adsorption. Consequently, SnO2-M achieved 2.2× higher degradation efficiency (61.09% in 3 h), with •OH and h+ as the dominant reactive species, highlighting microwave synthesis as a promising strategy for high-performance photocatalysts in environmental remediation.