Relationship between Synthesis Conditions and Photocatalytic Activity of Nanocrystalline TiO₂

Table 1

Results for the photodecomposition of methylene blue using the nanocrystalline TiO₂ powders synthesized at various conditions.

	Sample	Adsorption amount^a (mg g^−1)	First-order reaction rate constant (𝑘)^b (h^−1)	Decomposition ratio^c (—)
	P25	0.80	0.536	0.460
Molar ratio^d (—)	2	0.41	0.295	0.263
	5	1.10	0.690	0.538
	10	1.21	0.786	0.621
	20	1.68	0.846	0.640
	50	2.02	0.873	0.657
pH^e	2.5	1.03	0.894	0.658
	4	0.92	0.864	0.641
	7	1.10	0.690	0.538
	9	0.85	0.588	0.480
	11	1.46	0.551	0.440
Temperature^f (^°C)	400	2.37	0.516	0.395
	500	1.21	0.431	0.357
	600	1.10	0.690	0.538
	700	0.98	0.871	0.614
	800	0.22	0.701	0.515
	900	0.20	0.468	0.376
	1000	0.20	0.511	0.385

^aAmount of methylene blue adsorbed for first 30 min (refer to the adsorption zone in Figures 1, 5, and 8).
^bValue determined by fitting the data for the photolysis zone in Figures 1, 5, and 8 to first-order reaction.
^cRatio between degraded and initial amounts.
^dOther synthesis conditions are as follows: pH = 7 and calcination temperature = 600 ^°C.
^eOther synthesis conditions are as follows: molar ratio = 5 and calcination temperature = 600 ^°C.
^fOther synthesis conditions are as follows: molar ratio = 5 and pH = 7.