Preparation of mesoporous TiO 2 /g-C 3 N 4 heterojunction catalyst and visible-light-driven photocatalytic reduction of Cr 6+

Combining TiO 2 and graphitic carbon nitride (g-C 3 N 4 ) into TiO 2 /g-C 3 N 4 heterojunction catalyst is an effective way to narrow band gap of TiO 2 , inhibit recombination of photoinduced carriers and improve photocatalytic efficiency. Mesoporous TiO 2 /g-C 3 N 4 heterojunction was synthesized with a sol-gel method and characterized by SEM, TEM, XRD, BET, XPS, UV -Vis DRS, PL spectrum and electrochemical technologies. UV -Vis DRS displayed that band gap of TiO 2 /g-C 3 N 4 was 2.64 eV which was narrower than that of TiO 2 and g-C 3 N 4 , suggesting that TiO 2 /g-C 3 N 4 can produce photoinduced carriers under visible light. BET showed that specific surface area of TiO 2 /g-C 3 N 4 was 137.06 m 2 center dot g - 1 . Furthermore, I -t curve, Mott-Schottky curve and PL spectrum all proved that photocurrent of TiO 2 /g-C 3 N 4 was higher than that of TiO 2 , revealing that introduction of g-C 3 N 4 accelerated the transfer of photoelectrons and restrained the recombination of photo induced carriers. Under the optimal conditions (mass ratio of g-C 3 N 4 to TiO 2 was 1:5, TiO 2 /g-C 3 N 4 dosage was 1.6 g center dot L -1 , pH value was 5, Cr 6+ initial concentration was 1 mg center dot L -1 ), the removal of Cr 6+ reached 98 %. XPS analysis proved that Cr 6+ was adsorbed and then reduced to Cr 3+ on TiO 2 /g-C 3 N 4 surface in situ, and main reactants for reducing Cr 6+ were electrons and center dot O 2 - detected via radical scavenging tests. Moreover, photocatalytic reduction kinetics equation was established based on Langmuir-Hinshelwood (H -L) model and apparent reaction rate ( K app ) constant was calculated. TiO 2 /g-C 3 N 4 showed a satisfied stability and photocatalytic reduction of Cr 6+ still maintained 85 % after seven cycles, demonstrating that TiO 2 /g-C 3 N 4 had a potential application to remove Cr 6+ .