Averrhoa carambola: A Renewable Source of Oxalic Acid for the Facile and Green Synthesis of Divalent Metal (Fe, Co, Ni, Zn, and Cu) Oxalates and Oxide Nanoparticles

Table 3

Thermal decomposition temperatures and weight loss.

(a)

	First weight loss			Second weight loss
	Temp (°C)	Obs. (%)	Calc. (%)	Temp. (°C)	Obs. (%)	Calc. (%)	Possible formed
FeC2O4·2H2O	170–218	20.9	20.95	242–330	35.7	40.03	FeO
						35.59	Fe2O3
						37.07	Fe3O4
CoC2O4·2H2O	170–232	19.3	19.69	350–436	39.7	39.36	CoO
						34.99	Co2O3
						36.44	Co3O4
NiC2O4·2H2O	210–285	20.6	19.72	370–434	41.9	39.41	NiO
ZnC2O4·2H2O	132–198	17.8	19.02	385–445	38.9	38.02	ZnO

(b)

	Sloppy weight loss				Sharp weight loss
	Temp. (°C)	Obs. (%)	Calc. (%) depends on		Temp. (°C)	Obs. (%)	Calc. (%) depends on
CuC2O4·xH2O	272	3.8	= 0	0	272–360	54.4	= 0	46.89	CuO
			= 1	21.25			= 1	42.47
			= 0.3	3.92			= 0.3	55.5	Cu