Well-designed polymer-grafted and heteroatom co-doped carbon nitride quantum dots: Towards efficient friction-reduction and anti-wear additives

Abstract

Water-based lubricants are rising rapidly again in lubrication owing to their eco-friendly, low-cost, and extensive source in the context of escalating global energy crises and environmental degradation. Nevertheless, the weak anti-reduction and anti-wear behaviors of water-based lubricants have emerged as the critical bottlenecks restricting their development. Consequently, the new-type polyacrylic acid (PAA)-grafted carbon nitride quantum dots (X-CNQDs-PAAn) with co-doping by B and P were first synthesized and directly applied as additives in water-based lubricants (X representing the doped atoms of B and P; n representing the molecular weight of PAA was 2000, 3000, and 5000). The surface and core dual-designed X-CNQDs-PAAn could remarkably promote the lubricity of the base liquid; among them, B,P-CNQDs-PAA2000 exhibited the best efficacy. Specifically, adding 1.5 wt% of B,P-CNQDs-PAA2000, the friction-reduction and anti-wear performances of the base liquid can be maximally increased by 48.04 % and 85.3 %, respectively. Experimental results demonstrated that the grafted PAA groups and co-doped B and P have a pronounced effect on enhancing the tribological behaviors of CNQDs-based additives. Additionally, B,P-CNQDs-PAA2000 still possessed good tribological performances under harsh operational conditions such as high-load and long duration. The outstanding tribological behaviors of B,P-CNQDs-PAA2000 are mainly attributed to they could form a thick and tight tribo-film on the frictional interfaces. Noteworthily, the embedded B,P-CNQDs-PAA2000 in the tribo-film played a significant role in improving its strength and thickness.