Sodium Dialkyldithiophosphate-Assisted Hydrothermal Synthesis of the MoS₂ Microspheres and its Photocatalytic Degradation of Rhodamine B

We employed new sulfur source, NaDDP to synthesis MoS₂ microspheres through hydrothermal methods and investigated its photocatalytic activity of MoS₂ for degradation of rhodamine B under various conditions.

Molybdenum disulfide (MoS₂) is a layered semiconductor composed of three layers of covalently bonded S–Mo–S, and the three layers (S–Mo–S) can be arranged in the following way: hexagon (2H-MoS₂), diamond (3R-MoS₂) and triangle (1T-MoS₂). However, the 2H-MoS₂ is an indirect band gap semiconductor with a band gap in the range of 1.2–1.8 eV, which is an ideal visible light induced photocatalyst for high solar energy utilization efficiently.

The MoS₂ microspheres were synthesized through hydrothermal methods by employing ammonium molybdate, sodium dialkyldithiophosphate and oxalic acid.

Figure 1 shows the photocatalytic activity of MoS₂ microshperes under visible-light irradiation with the concentration of oxalic acid. During the 120 min reaction under visible-light irradiation, the dye degradation percentage varied according to the concentration of oxalic acid as follows: A3 (91.3%) > A4 (88.6%) > A2 (80.1%) > A1 (61.0%). The photocatalytic degradation of rhodamine B followed first-order kinetics. The rate constants for A1, A2, A3 and A4 were estimated to be 0.0065, 0.011, 0.016 and 0.015 min-1, respectively. These results showed that A3 exhibited the highest photocatalytic activity under visible-light irradiation.

Fig. 1. Photocatalytic degradation of rhodamine B by A1, A2, A3, A4 (a), and kinetic fit for rhodamine B with A1, A2, A3, A4 (b); k—rate constant, t1/2—half-life time; C and C0—measured and initial concentrations.(A1: 0mol/L, A2:0.375mol/L), A3: 0.075mol/L, A4: 0.1125mol/L)

Fig. 2 shows the photocatalytic degradation of rhodamine B using MoS₂ microshperes prepared at different sulfur sources: NaDDP(MoS₂-1), thiourea(MoS₂-2), thioaceteamide(MoS₂-3) and L-cysteine(MoS₂-4). 41.3% of rhodamine B was adsorbed onto MoS₂-1, while 18.5, 27.3 and 21.2% of rhodamine B was adsorbed onto MoS₂-2, MoS₂-3 and MoS₂-4, respectively. The degradation efficiency varied according to the sulfur sources as follows: MoS₂-1 (91.3%) > MoS₂-3 (81.3%) > MoS₂-4 (77.1%) > MoS₂-2 (70.0%). The rate constant (k) for MoS₂-1, MoS₂-2, MoS₂-3 and MoS₂-4 were estimated to be 0.01638, 0.00667, 0.00925 and 0.00767 min–1, respectively. These results showed that when NaDDP is used as a sulfur source, the best photocatalytic performance is achieved.

Fig. 2. Photocatalytic degradation of rhodamine B by MoS₂-1, MoS₂-2, MoS₂-3, MoS₂-4 (a), and kinetic fit for rhodamine B with MoS₂-1, MoS₂-2, MoS₂-3, MoS₂-4 (b); k is the rate constant, t1/2 is the half-life time; C and C0 are measured and initial concentrations.(MoS₂-1: NaDDP, MoS₂-2: thiourea, MoS₂-3: thioactamide, MoS₂-4: L-cysteine)

Our results of this study were published in Journal "Kinetics and Catalysts" under the title of "Photocatalytic Degradation of Rhodamine B on MoS₂ Microspheres Prepared by Sodium Dialkyldithiophosphate-Assisted Hydrothermal Synthesis"(https://doi.org/10.1134/s00231-584-2303-0024).