▎ 摘　　要

NOVELTY - Preparing graphene oxide comprises (i) adding graphite sheet into three-necked flask, adding concentrated sulfuric acid, sodium persulfate and phosphorus pentoxide, stirring, cooling to room temperature, adding water, centrifuging to neutral and vacuum drying to obtain solid pre-oxidized graphite, and (ii) adding pre-oxidized graphite flake into the three-necked flask, adding concentrated sulfuric acid, dropping potassium permanganate, heating, adding water and hydrogen peroxide, washing, centrifuging and ultrasonic processing to form graphene oxide solution. USE - The graphene oxide is useful as near infrared fluorescent probe for detecting pH of water sample (claimed), and detecting and imaging solution or water sample. ADVANTAGE - The graphene oxide has upconversion property (claimed), and has good water solubility. The method produces high yield. DETAILED DESCRIPTION - Preparing graphene oxide comprises (i) adding 1.5 g graphite sheet into three-necked flask, adding 6 ml concentrated sulfuric acid, 1.2 g sodium persulfate and 1.25 g phosphorus pentoxide, stirring for 4.5 hours at 50-80 degrees C, cooling to room temperature, adding 250 ml high pure water, placing for night, centrifuging to neutral and vacuum drying at 35 degrees C to obtain solid pre-oxidized graphite, and (ii) adding 0.5 g pre-oxidized graphite flake into the three-necked flask at 0 degrees C, adding 12-20 ml concentrated sulfuric acid, dropping 2.5 g potassium permanganate, heating to 35 degrees C, stirring for 2-5 hours, dropping 45 ml high pure water, stirring for 2 hours, adding 120 ml high pure water and 4 ml hydrogen peroxide, washing using 1l of 1:10 hydrochloric acid, centrifuging, washing using high pure water, centrifuging to neutral, and ultrasonic processing to form graphene oxide solution. An INDEPENDENT CLAIM is also included for use method of the graphene oxide in pH indication, comprising (i) taking out 5 ml graphene oxide solution, vacuum drying at 35 degrees C and preparing into specific concentration of graphene oxide solution, (ii) taking 10 ml graphene oxide solution and diluting for 2-5 times to obtain different concentration graphene oxide solutions, and (iii) adjusting pH of the different concentration diluted graphene oxide solutions to 2-12 using dilute hydrochloric acid and sodium hydroxide, so that the fluorescence intensity of the system is gradually reduced from pH 2-12, luminescence center has no obvious change and fluorescence intensity and pH value has good linearity at 850 nm, and suggesting that water-soluble graphene oxide can be used as near infrared fluorescent probe pH indicator.