Synthesis · General Synthesis of Mixed Semiconducting Metal Oxide Hollow Spheres with Tunable Compositions for Low-Temperature Chemiresistive Sensing

8 structured synthesis routes

Completeness describes how fully the route could be reconstructed from the main article and supporting information.

Complete recipeSource: SI

Route 1: Hydrothermal

S-1 to S-2 · 1.2 and 1.3

Metal precursorsFeSO4.7H2O (0.067 g) and Co(NO3)2.6H2O (0.033 g) in 2 mL aqueous solution

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127 (0.2 g), ammonia solution 25-28 wt% (0.5 mL), formaldehyde solution 37 wt% (0.38 mL)

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Time1 h initial stirring; 24 h after TA/formaldehyde addition; 12 h after metal addition; 12 h hydrothermal; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Scalability contextGeneral route extended to binary, ternary and quinary compositions by changing metal salts and mass ratios.

Show 8 structured reagent records

Role	Reagent	Amount / concentration	Source
Additive	Pluronic F127	0.2 g	S-1 to S-2 · 1.2 and 1.3
Solvent	water	46 mL	S-1 to S-2 · 1.2 and 1.3
Solvent	ethanol	8 mL	S-1 to S-2 · 1.2 and 1.3
Base	ammonia solution	0.5 mL · 25-28 wt%	S-1 to S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-1 to S-2 · 1.2 and 1.3
Additive	formaldehyde solution	0.38 mL · 37 wt%	S-1 to S-2 · 1.2 and 1.3
Metal Source	FeSO4.7H2O	0.067 g	S-1 to S-2 · 1.2 and 1.3
Metal Source	Co(NO3)2.6H2O	0.033 g	S-1 to S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 2: Hydrothermal

S-2 · 1.2 and 1.3

Metal precursorsNi(NO3)2.6H2O, Co(NO3)2.6H2O, FeSO4.7H2O, Cu(NO3)2.3H2O and Zn(NO3)2.6H2O; total metal source 0.1 g; mass ratio 1:1:1:1:1

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127 (0.2 g), ammonia solution (0.5 mL), formaldehyde solution (0.38 mL)

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Timesame as Fe-Co-TA procedure; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Scalability contextQuinary route uses five different metal salts in equal mass ratio.

Show 9 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	Ni(NO3)2.6H2O	part of total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Co(NO3)2.6H2O	part of total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	FeSO4.7H2O	part of total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Cu(NO3)2.3H2O	part of total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Zn(NO3)2.6H2O	part of total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-2 · 1.2 and 1.3
Additive	Pluronic F127	0.2 g	S-2 · 1.2 and 1.3
Base	ammonia solution	0.5 mL · 25-28 wt%	S-2 · 1.2 and 1.3
Additive	formaldehyde solution	0.38 mL · 37 wt%	S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 3: Hydrothermal

S-2 · 1.2 and 1.3

Metal precursorsNi(NO3)2.6H2O, Co(NO3)2.6H2O and Mn(NO3)2.6H2O; total metal source 0.1 g; mass ratio 1:1:1

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127, ammonia solution, formaldehyde solution

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Timesame as Fe-Co-TA procedure; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Show 4 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	Ni(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Co(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Mn(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 4: Hydrothermal

S-2 · 1.2 and 1.3

Metal precursorsNi(NO3)2.6H2O and Co(NO3)2.6H2O; total metal source 0.1 g; mass ratio Ni:Co = 2:1

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127 (0.2 g), ammonia solution (0.5 mL), formaldehyde solution (0.38 mL)

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Timesame as Fe-Co-TA procedure; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Show 6 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	Ni(NO3)2.6H2O	part of total 0.1 g · mass ratio Ni:Co 2:1	S-2 · 1.2 and 1.3
Metal Source	Co(NO3)2.6H2O	part of total 0.1 g · mass ratio Ni:Co 2:1	S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-2 · 1.2 and 1.3
Additive	Pluronic F127	0.2 g	S-2 · 1.2 and 1.3
Base	ammonia solution	0.5 mL · 25-28 wt%	S-2 · 1.2 and 1.3
Additive	formaldehyde solution	0.38 mL · 37 wt%	S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 5: Hydrothermal

S-2 · 1.2 and 1.3

Metal precursorsNi(NO3)2.6H2O, Co(NO3)2.6H2O and Zn(NO3)2.6H2O; total metal source 0.1 g; mass ratio 1:1:1

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127, ammonia solution, formaldehyde solution

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Timesame as Fe-Co-TA procedure; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Show 4 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	Ni(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Co(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Metal Source	Zn(NO3)2.6H2O	part of total 0.1 g · 1:1:1 mass ratio	S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 6: Hydrothermal

S-2 · 1.2 and 1.3

Metal precursorsNi(NO3)2.6H2O and Zn(NO3)2.6H2O; total metal source 0.1 g; mass ratio Ni:Zn = 1:2

Linker precursorstannic acid (0.2 g)

Solventswater (46 mL) and ethanol (8 mL)

AdditivesPluronic F127, ammonia solution, formaldehyde solution

Atmospherehydrothermal sealed autoclave; final calcination in air

Temperature100 C hydrothermal; 400 C calcination

Timesame as Fe-Co-TA procedure; 2 h calcination

Oxidant / reductantair during calcination

Work-upcollected by centrifugation, washing and drying before calcination

Activationcalcination in air at 400 C for 2 h, ramp 2 C/min

Show 4 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	Ni(NO3)2.6H2O	part of total 0.1 g · mass ratio Ni:Zn 1:2	S-2 · 1.2 and 1.3
Metal Source	Zn(NO3)2.6H2O	part of total 0.1 g · mass ratio Ni:Zn 1:2	S-2 · 1.2 and 1.3
Linker	tannic acid	0.2 g	S-2 · 1.2 and 1.3
Additive	Pluronic F127	0.2 g	S-2 · 1.2 and 1.3

Complete recipeSource: SI

Route 7: Drop Cast

S-3 · 1.5 Gas sensing performance

Metal precursorsNi-Co-Fe-Cu-Zn-TA-400 metal oxide nanoparticles

Linker precursorsnone

Solventsethanol used to form paste

Atmosphereair / room temperature drying; calcination atmosphere not explicitly stated for device

Temperatureroom temperature drying; 300 C device calcination; 100 C ageing

Time1 h device calcination; 5 days ageing

Substrate orientationalumina tube with Au electrodes and inserted Ni-Cr heater wire

Work-uppaste coating, drying, calcination, insertion of heater wire

Activationaged at the optimal operating temperature (100 C) for five days before measurement

Show 4 structured reagent records

Role	Reagent	Amount / concentration	Source
Other	metal oxide nanoparticles	Not specified	S-3 · 1.5 Gas sensing performance
Solvent	ethanol	Not specified	S-3 · 1.5 Gas sensing performance
Other	alumina tube with Au electrodes	Not specified	S-3 · 1.5 Gas sensing performance
Other	Ni-Cr alloy wire	Not specified	S-3 · 1.5 Gas sensing performance

Complete recipeSource: SI

Route 8: Hydrothermal

S-2 · 1.3 Synthesis of mixed metal oxide hollow spheres

Metal precursorssame quinary MPCP precursor as Ni-Co-Fe-Cu-Zn-TA-400

Linker precursorstannic acid

Solventswater and ethanol

AdditivesPluronic F127, ammonia, formaldehyde

Atmosphereair during calcination

Temperature300-400 C investigated; 350 C sample explicitly imaged; 450 C collapse noted in main text

Time2 h calcination for standard MOHS synthesis

Oxidant / reductantair

Work-upas for quinary route

Activationcalcination at selected temperature

Show 2 structured reagent records

Role	Reagent	Amount / concentration	Source
Metal Source	quinary metal salts	total 0.1 g · 1:1:1:1:1 mass ratio	S-2 · 1.3 Synthesis of mixed metal oxide hollow spheres
Linker	tannic acid	0.2 g	S-2 · 1.3 Synthesis of mixed metal oxide hollow spheres