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Time-dependent wet-processing of HiPCo nanotubes in ~ 0.5 M phosphoric acid and its effect on the structural, transport, infrared light absorption and photoconduction characteristics have been studied. Nanotubes were treated for nominal time intervals of 1, 2 and 3 h. The treatment is found to be a two-step process that initially results in the removal/partial replacement of most pre-existing C-O, O–H and CH_x groups with phosphorous oxy and carbonyl groups. According to T-dependent current–voltage measurements, the differential conductance, G of nanotube network varies with temperature as ~ T^a, with a exhibiting a slight increase as a result of the treatment, attributed to a slight increase in disorder and not doping effects. The nanotubes processed for three hours also show an order of magnitude improvement in photoconduction response time compared to that of untreated tubes, with growth/decay characteristic time constants approaching a sub-second range.