70
4 Synthesis of Two-Dimensional (2D) Nanomaterials
4.4.2 Transition Metal Nitrides
Only a few 2D nitrides including MoN (Xie et al. 2014), GaN (Al Balushi et al. 2016),
Ti 4 N 3 (Urbankowski et al. 2016), and Ti 2 N (Soundiraraju and George 2017) have
been reported so far. Current strategies for synthesis of 2D nitrides are mostly limited
to exfoliation of layered materials, while a gas-phase synthesis of GaN monolayers
under graphene also exists (Al Balushi et al. 2016). Several of those studies, however,
lacked focus on upscaling the methods and yielding 2D metal nitrides which could
be easily be implemented into devices.
Heat treatment in ammonia (ammoniation) has been used on metal oxides to
either N-dope them or transform oxides to 3D nitrides. Although ammoniation of
2D precursors such as GaSe to yield the 2D metal nitride GaN has been reported, the
extent of the route of synthesizing other potential 2D metal nitrides via ammoniation
has not been fully realized (Sreedhara et al. 2014). TiO 2 can be N-doped by nitridation at 600 °C (Sakthivel and Kisch 2003; Liu et al. 2009), and recently reported
nitridation attempts of Ti 3 C 2 have yielded only N-doped 2D carbides. Ti 3 C 2 was
doped with nitrogen atoms by ammoniation at temperatures up to 700 °C in which N
comprised up to 20.7 at % of the product (Wen et al. 2017). It was only recently when
synthesis of 2D metal nitrides via ammoniation was reported, including 2D MoN
via the ammoniation of MoO 3 -coated NaCl (Xiao et al. 2017). Urbankowski et al.
(2017) report the first transformation of Mo 2 CT x and V 2 CT x carbide MXenes into 2D
metal nitrides via ammoniation at 600 °C. To synthesize nitride MXenes, multilayer
powders and delaminated films of Mo 2 CT x and V 2 CT x were treated at 600 °C for
1 h at a heating rate of 10 °C h
−1 in an ammonia, NH 3 , atmosphere and cooled at the
same rate. The ammonia flow rate through the reactor was approximately 300 cm
3
min
−1 . During the reaction, nitridation occurs by the replacement of C atoms, in the
Mo 2 CT x and V 2 CT x , with N atoms. A schematic of the procedure is displayed in
Fig. 4.4d. It is important to note that unlike previously reported 2D MoN and V 2 N via
salt-templated synthesis with 2D metal oxide precursors (Xiao et al. 2016a, b), the
2D metal nitrides reported here, synthesized with carbide MXene precursors, have
different crystal structures than those previously reported. Their results demonstrate
that Mo 2 N retains the structure of MXene and V 2 C transforms into a mixed layered
structure of trigonal V 2 N and cubic VN.
4.4.3 Transition Metal Carbonitrides
Zhi et al. (2017) developed a one-step and environmental benign ion-thermal route
to synthesize 2D hierarchical Mo 2 C/C-N hybrid using (NH 4 ) 6 Mo 7 O 24 4H 2 O as a
molybdenum source, dicyanodiamine (C 2 H 4 N 4 ) as a carbon and nitrogen source,
and NH 4 Cl as a 2D structural oriented and ion-thermal agent. As expected, the assynthesized 2D hierarchical Mo 2 C/C-N hybrid is composed of well-dispersed Mo 2 C
nanocrystals decorated on nitrogen-doped carbon (C-N) frameworks and possesses
4 Synthesis of Two-Dimensional (2D) Nanomaterials
4.4.2 Transition Metal Nitrides
Only a few 2D nitrides including MoN (Xie et al. 2014), GaN (Al Balushi et al. 2016),
Ti 4 N 3 (Urbankowski et al. 2016), and Ti 2 N (Soundiraraju and George 2017) have
been reported so far. Current strategies for synthesis of 2D nitrides are mostly limited
to exfoliation of layered materials, while a gas-phase synthesis of GaN monolayers
under graphene also exists (Al Balushi et al. 2016). Several of those studies, however,
lacked focus on upscaling the methods and yielding 2D metal nitrides which could
be easily be implemented into devices.
Heat treatment in ammonia (ammoniation) has been used on metal oxides to
either N-dope them or transform oxides to 3D nitrides. Although ammoniation of
2D precursors such as GaSe to yield the 2D metal nitride GaN has been reported, the
extent of the route of synthesizing other potential 2D metal nitrides via ammoniation
has not been fully realized (Sreedhara et al. 2014). TiO 2 can be N-doped by nitridation at 600 °C (Sakthivel and Kisch 2003; Liu et al. 2009), and recently reported
nitridation attempts of Ti 3 C 2 have yielded only N-doped 2D carbides. Ti 3 C 2 was
doped with nitrogen atoms by ammoniation at temperatures up to 700 °C in which N
comprised up to 20.7 at % of the product (Wen et al. 2017). It was only recently when
synthesis of 2D metal nitrides via ammoniation was reported, including 2D MoN
via the ammoniation of MoO 3 -coated NaCl (Xiao et al. 2017). Urbankowski et al.
(2017) report the first transformation of Mo 2 CT x and V 2 CT x carbide MXenes into 2D
metal nitrides via ammoniation at 600 °C. To synthesize nitride MXenes, multilayer
powders and delaminated films of Mo 2 CT x and V 2 CT x were treated at 600 °C for
1 h at a heating rate of 10 °C h
−1 in an ammonia, NH 3 , atmosphere and cooled at the
same rate. The ammonia flow rate through the reactor was approximately 300 cm
3
min
−1 . During the reaction, nitridation occurs by the replacement of C atoms, in the
Mo 2 CT x and V 2 CT x , with N atoms. A schematic of the procedure is displayed in
Fig. 4.4d. It is important to note that unlike previously reported 2D MoN and V 2 N via
salt-templated synthesis with 2D metal oxide precursors (Xiao et al. 2016a, b), the
2D metal nitrides reported here, synthesized with carbide MXene precursors, have
different crystal structures than those previously reported. Their results demonstrate
that Mo 2 N retains the structure of MXene and V 2 C transforms into a mixed layered
structure of trigonal V 2 N and cubic VN.
4.4.3 Transition Metal Carbonitrides
Zhi et al. (2017) developed a one-step and environmental benign ion-thermal route
to synthesize 2D hierarchical Mo 2 C/C-N hybrid using (NH 4 ) 6 Mo 7 O 24 4H 2 O as a
molybdenum source, dicyanodiamine (C 2 H 4 N 4 ) as a carbon and nitrogen source,
and NH 4 Cl as a 2D structural oriented and ion-thermal agent. As expected, the assynthesized 2D hierarchical Mo 2 C/C-N hybrid is composed of well-dispersed Mo 2 C
nanocrystals decorated on nitrogen-doped carbon (C-N) frameworks and possesses