Nitrogen-Doped Carbon Dots/2D Nickel-Benzene-1,4-Dicarboxylate Metal–Organic Framework Nanocomposites as Stabilizers for Pickering Emulsion Lubricants

Owing to their excellent stability and environmental friendliness, Pickering emulsions hold great promise as alternatives to water-based cutting fluids (WCF). Herein, we successfully constructed a nitrogen-doped carbon quantum dots (N-CDs)/two-dimensional nickel-benzene-1,4-dicarboxylate metal–organic framework (2D Ni-BDC) nanocomposite using an impregnation and microwave-assisted drying method. The makeup and composition of the N-CDs/2D Ni-BDC nanocomposite were analyzed through a range of methods. Based on contact angle measurements, the nanocomposite exhibited appropriate hydrophilicity and lipophilicity, enabling the formation of a stable Pickering emulsion stabilized by N-CDs/2D Ni-BDC. The architecture and makeup of emulsions containing different concentrations of the nanocomposite were elucidated via multiple characterization techniques. The tribological performance of the N-CDs/2D Ni-BDC-stabilized Pickering emulsion was examined via a reciprocating friction tester, primarily investigating how nanocomposite concentration and friction duration influence its properties. It was found that the concentration of N-CDs/2D Ni-BDC has a notable effect on the friction coefficient and wear rate of the emulsion. When compared with pure water, the friction coefficient and wear rate were reduced by 66% and 69%, respectively. Additionally, the average friction coefficient and wear rate of the N-CDs/2D Ni-BDC-PK emulsion were also 20.4% and 8.0% lower than those of the 2D Ni-BDC-PK emulsion. XPS analysis of the worn surface revealed the presence of the collaborative lubrication effect from the nanocomposite, which primarily included tribofilm formation and interlayer sliding.