2D/1D graphitic carbon nitride/titanate nanotubes heterostructure for efficient photocatalysis of sulfamethazine under solar light: Catalytic “hot spots” at the rutile–anatase–titanate interfaces

•2D/1D g-C3N4/TNTs composite was developed and showed high photocatalytic activity.•P25-type titania decorated on TNTs after in situ transformation of titanate.•Hot spots at rutile–anatase–titanate interfaces led to efficient electron transfer.•Heterostructure with g-C3N4 extended the adsorption to visible light region.•SMT sites with high Fukui nucleophilic index exhibited high reactivity.