Foam is a gas-liquid dispersion system in which the gas is the dispersed phase, and the water serves as the continuous medium [1]. In recent years, foam has received significant attention due to its wide range of applications. For instance, in the oil industry, foam acts an important role in drilling, fracturing, and enhanced oil recovery due to the advantages of reducing energy consumption, increasing well stability, reducing environmental pollution, and improving operational safety [[2], [3], [4]]. In the food science, foam plays a crucial role in enhancing the texture and taste of cream, ice cream, and cakes [5,6]. In the field of materials science and engineering, foam enables the design of new materials with desirable properties such as thermal insulation, shock absorption, and sound absorption [[7], [8], [9], [10], [11], [12]]. In the medical field, foam is widely used in drug delivery, tissue engineering, and medical imaging [[13], [14], [15]].

Foam is composed of bubbles divided by a liquid film. Various formation methods, including mechanical stirring [16,17], gas foaming [18], chemical foaming [19], physical foaming [20], and biofoaming [21], have been reported. These methods involve injecting gas into a solution or surfactant solution to form foam. From a dynamic perspective, foam is a thermodynamically unstable system. Its stability is affected by internal factors, such as foam drainage, bubble coalescence, and gas diffusion, as well as external conditions, such as temperature, pressure, shear, and the gas used for foaming. Therefore, the stability of foam, as a key index affecting its effectiveness, directly affects its potential application in related fields.

Traditionally, the foam stabilized solely by a foaming agent has the disadvantages of fast drainage rate and low strength. To enhance foam stability, it is usually necessary to add a variety of surfactants, polymers, and solid nanoparticles. Compared with traditional surfactant- stabilized foam or polymer-stabilized foam, nanoparticle-stabilized foam (especially the biomass-derived nanoparticle-stabilized foam) offers unique advantages, e.g., lower dosage, cost, and toxicity, as well as superior sustainability, biocompatibility, and environmental impact. In addition, the nanoparticles can form an irreversible and dense interfacial film at the liquid-gas interface, which can not only greatly improve the stability of the foam, but also impart the foam special properties. Therefore, nanoparticles have received increasing attention as foam stabilizers, and of the as-prepared foam stabilized by nanoparticles is referred to as Pickering foam.

The history of Pickering foam can be dated back to the beginning of the 20th century. In 1904, Ramsden [22] first founded that in a large number of non-protein colloid solutions, solid particles can be formed as a coating of similar solid or high viscosity substances on the liquid interface. The formed emulsion can be permanently stabilized, and thereby the presence of solids on the surface of bubble must contribute significantly to its persistence. In 1907, Pickering conducted a systematic study on emulsions stabilized by solid particles as emulsifiers. Such emulsions were later called Pickering emulsions, and foam stabilized by solid particles was also called Pickering foam [23]. As early as 1925, in mineral frothers and ore flotation, Bartsch [24] revealed that partially hydrophobic particles played critical roles in stabilization of foam, while completely wetted particles had no effect on the stability of particles. In 1974, Hausen [25] demonstrated that the stable foam structure can be formed by using various metal oxides and clay particles as solid emulsifiers through proper surface modification revealed by microscopic observation. Tang et al. [26]. first demonstrated that hydrophobic silica particles had good stabilization for foams produced by using sodium dodecyl sulfate as foaming agent in an alkaline aqueous media. The higher the concentration of SiO2, the smaller the particle size is, the higher the stability of the foam is. Cervin et al. [27] first used surface modified CNFs to stabilize aqueous foam, and then dried it to produce a lightweight porous cellulose material. The advantage of using CNFs to stabilize foam is that it is renewable and degradable, and the stability of the foam is significantly increased compared to other types of foam stabilizers. Tzoumaki et al. [28] studied for the first time the possibility of ChNCs extracted from shrimp shells as colloidal rod-like particles to stabilize aqueous foam. At low concentrations of ChNCs (i.e., <0.4 wt%), the foam can effectively stabilize the foam within 3 h. At high concentrations of ChNCs (i.e., >1 wt%), the foam can be stable for more than a few days. Rodriguez et al. [29] first studied the foaming properties and interfacial properties of Green tea polyphenols-whey proteins nanoparticles. After the addition of polyphenols, the interface film of the foam is worse, and the liquid is eliminated faster in the same time period, but it can maintain its shape for a long time. In general, the addition of various types of nanoparticles can significantly improve the stability of the foam and expand its application range by adjusting the foam properties. However, the cost, toxicity, and environmental impact of nanoparticles need to be considered in practical applications. Therefore, the biomass-derived nanomaterials, e.g., cellulose nanomaterials, chitin nanomaterials, and protein nanoparticles have gained more attention as promising alternatives in the development of sustainable and eco-friendly Pickering foam systems in recent years [30,31]. Nevertheless, the excellent properties of Pickering foam stabilized by various types of nanoparticles are of great significance in advancing the application of functional foam systems and promoting the sustainable development of related technical fields [32]. However, the mechanisms of action for Pickering foams stabilized by different types of nanoparticles are different from those of surfactants, and the application directions are different. Therefore, a comprehensive overview of recent advances in Pickering foam stabilized by various nanoparticles is crucial. However, to the best of the authors' knowledge, there is currently a lack of a comprehensive review on this specific topic.

In this review, we present the latest advancements in stabilizing Pickering foams with different types of nanoparticles, including cellulose nanomaterials, chitin nanomaterials, nano-silica, protein nanoparticles, and other nanoparticle sources (Fig. 1). We discuss various preparation and surface modification methods of nanoparticles, and elucidate the mechanisms underlying the interaction between different types of nanoparticles and surfactants, polymers, and other functional additives in relation to the foam volume and stability. Then, we summarize the latest research progress of Pickering foam in the following areas: 1) oil industry; 2) food industry; 3) porous functional materials; and 4) foam flotation. Finally, we provide insights into the future directions for research and development of different types of nanoparticles as foam stabilizers in diverse industrial applications.