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Nd3+ ion modified TiO2 sol was prepared by chemical coprecipitation–peptization method. The sol particles were well distributed in colloid system and mean size was 10 nm by AFM analysis. Direct conversion of Nd3+–TiO2 sol particles from amorphous to semicrystalline phase was achieved at 62 °C and pH 1.0 with 12 h peptizing process. Photocatalytic reactivity of Nd3+–TiO2 sol was evaluated by photodegradation of phenol in solution under visible light irradiation. It was found that concentration decreased from initial 100 mg l−1 phenol to final 5.29 mg l−1 phenol and 75.2 mg l−1 phenol derivatives after 2 h photocatalysis This result indicates that Nd3+–TiO2 nanocolloids exhibited photocatalytic activity in the visible range. Meanwhile, total organic carbon (TOC) value declined from initial 37.1 mg l−1 to final 29.3 mg l−1, which indicates the weak capability of photomineralization, but the power of selective photocatalysis. The reaction mechanism of Nd3+–TiO2 sol photocatalysis was proposed as the process of self-sensitization and sub-bandgap overlapping. [Copyright &y& Elsevier]