A method of hydrogen generation from sodium borohydride (NaBH.sub.4) using zirconium dioxide/calcium silicate/graphitic carbon nitride (ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4) based nanocomposite includes hydrolyzing NaBH.sub.4 in the presence of a ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4 nanocomposite material, where the NaBH.sub.4 reacts with water to form hydrogen (H.sub.2) gas in the presence of the ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4 nanocomposite material as a catalyst. Further, the ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4 nanocomposite material includes spherical metal oxide nanoparticles including a ZrO.sub.2 phase and a CaSiO.sub.3 phase dispersed on a matrix of g-C.sub.3N.sub.4 nanosheets, where the spherical metal oxide nanoparticles have an average particle diameter in a range from 3 to 18 nm. Still further, the hydrolyzing proceeds with a hydrogen generation rate of greater than or equal to 200 mL.Math.min.sup.1.Math.g.sup.1.

A ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4 nanocomposite material includes spherical metal oxide nanoparticles which include a ZrO.sub.2 phase and a CaSiO.sub.3 phase dispersed on a matrix of g-C.sub.3N.sub.4 nanosheets. The spherical metal oxide nanoparticles have an average particle diameter in a range from 3 to 18 nanometers (nm). The ZrO.sub.2/CaSiO.sub.3/g-C.sub.3N.sub.4 nanocomposite material has a Brunauer-Emmett-Teller (BET) surface area greater than or equal to 55 square meters per gram (m.sup.2.Math.g.sup.1).

A method of producing hydrogen comprising hydrolyzing sodium borohydride (NaBH.sub.4) with water at a temperature of from about 20 to about 75 C. in the presence of a particulate crystalline nanocomposite catalyst, wherein the ratio by weight of sodium borohydride to the particulate crystalline nanocomposite catalyst is from about 1:1 to about 5:1. The particulate crystalline nanocomposite catalyst comprises: a monoclinic Bi.sub.2O.sub.3 crystalline phase; a CaSiO.sub.3 crystalline phase; and, a graphitic-C.sub.3N.sub.4 crystalline phase, wherein at least a fraction of the graphitic-C.sub.3N.sub.4 is in the form of mesoporous nanosheets.

A method of degrading organic contaminants disposed in an aqueous medium, the method including contacting the aqueous medium with a particulate crystalline nanocomposite and irradiating the aqueous medium with radiation having a wavelength of from about 100 to about 800 nm. The particulate crystalline nanocomposite includes: a monoclinic bismuth oxide (Bi.sub.2O.sub.3) crystalline phase; a calcium metasilicate (CaSiO.sub.3) crystalline phase; and, a graphitic-carbon nitride (g-C.sub.3N.sub.4) crystalline phase, wherein at least a fraction of the graphitic-C.sub.3N.sub.4 is in the form of mesoporous nanosheets.

A method of water purification includes mixing contaminated water with a zirconium dioxide (ZrO.sub.2)/calcium silicate (CaSiO.sub.3)/graphitic carbon nitride (g-C.sub.3N.sub.4) based nanocomposite material to form a reaction mixture, further exposing the resultant reaction mixture to light, and removing the nanocomposite material to form purified water. The nanocomposite material consists of spherical metal oxide nanoparticles including a ZrO.sub.2 phase and a CaSiO.sub.3 phase dispersed on a matrix of g-C.sub.3N.sub.4 nanosheets, where the spherical metal oxide nanoparticles have an average particle diameter in a range from 2-25 nanometer (nm), and the nanocomposite material has a band gap energy in a range from 1.5-4 electron volt (eV).