NOVELTY - A carboxylated carbon nanotube catalyst carrier is prepared by mixing carbon nanotubes, concentrated nitric acid, and concentrated sulfuric acid with volume ratio of 1:3-3:2, performing reflowing treatment at 80-95 degrees C for 100-120 minutes, washing, and drying.    USE - Preparation of carboxylated carbon nanotube catalyst carrier for platinum/carbon nanotube catalyst used for preparing air cathode for microbial fuel cell (all claimed).    ADVANTAGE - Oxygen reduction effect of catalyst is improved, Pt/CNT catalyst prepared from catalyst carrier shortens start period of micro function circuit (MFC) and has high degree of crystallinity and small particle diameter, internal resistance of MFC is reduced, and output voltage is greatly increased.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) preparation of platinum/carbon nanotube (Pt/CNT) catalyst which involves subjecting catalyst carrier carboxylated carbon nanotubes chloride in ethanol solution which is mixed with molybdate to obtain carbon slurry, adding 0.2 mol/L sodium hydroxide (NaOH) solution to adjust pH value of solution to 7.5, adding excess 0.1 mol/L formaldehyde (HCHO), reducing for 2 hours at 80 degrees C, filtering, washing solution with silver nitrate (AgNO3) solution for leaching test to detect chlorine ion (Cl-), vacuum drying at 80 degrees C for 12 hours;    (2) preparation of air cathode which involves washing titanium wire net base material with 0.5 mol/L sulfuric acid (H2SO4) to remove oxide on surface, subjecting to ultrasonic treatment with acetone to remove oil in surface, performing ultrasonic cleaning with de-ionized water, coating 1 side of material with polytetrafluoroethylene (PTFE) which is diffusion layer, and coating other side with Pt/CNT catalyst; and    (3) operation process of air cathode microbial fuel cell which involves mixing pond bottom mud pre-culture solution as inoculum with amount of 1 g per L glucose with inoculated microbial fuel cell with volume ratio 1:1 in which mixing temperature is 30 degrees C, pre-culture solution contains 0.08 g per L ammonium chloride (NH4Cl), 0.04 g per L monopotassium phosphate (KH2PO4), 0.48 g per L yeast extract, and 5 ml per L trace element solution, and glucose nutrient solution contains 1 g per L glucose, 5 ml per L vitamin solution, 12.5 ml per L trace element, and 50 mmol per L poly(butylene styrene) (PBS).    DESCRIPTION OF DRAWING(S) - The drawing shows a spectrum diagram of CNT, CNT-80, and CNT-95. (Drawing includes non-English language text).