Solar energy is a renewable, green, and ecological energy source that has been favored by many scholars to address the shortage of freshwater resources (Li et al., 2020; Miao et al., 2019; Wang. et al., 2018). The use of solar energy to obtain clean freshwater by the purification of wastewater and seawater resources has become a popular research and development topic in academia and industry (Huang et al., 2018; Raza et al., 2018). Although considerable progress has been made, challenges remain in achieving simple, low-cost, green, and recyclable manufacturing protocols.
An absorber that converts solar energy into heat to produce steam is a crucial component for the design of a high-efficiency solar steam generation system, and commonly requires four features, namely, broadband solar absorbability, high photothermal efficiency, excellent thermal insulation to confine heat on the evaporation surface, and hydrophilic or porous structures for rapid water transportation (Xu et al., 2018). Among them, the full-band solar absorption capability is critical for efficient solar steam generation. Numerous carbon-based materials, including graphene oxide (GO) (Fu et al., 2017), carbon nanotubes (CNTs) (Chen. et al., 2017), and carbon black (Gao et al., 2019), have been used to achieve efficient solar steam generation to integrate them into solar steam generation for large-scale applications owing to their excellent solar collection capability, thermal stability, and environmental friendliness. For example, Yang et al. (2018) stabilized Chinese ink of a carbon-based paint using atomic layer deposition (ALD) and demonstrated the potential of an ALD/Chinese ink coating that exhibited powerful and wide solar absorption from the near-infrared (NIR) to ultraviolet (UV) regions. Moreover, GO (Hu et al., 2017; Ito et al., 2015; Wang et al., 2016) and CNTs (Chen et al., 2017; Wang et al., 2016; Yang et al., 2018) have been fabricated as films, foams, or sponges and applied to solar steam generation because of their strong and extensive solar absorption ability. Despite the significant progress made in the development of functionalized absorbers through recent efforts, significant challenges remain as these reported materials have drawbacks, such as complex manufacturing processes and high production costs, that hinder their practical use. Therefore, there is an urgent need to implement a new approach to develop cost-effective absorbers with high performance and simple manufacturing processes.
Discarded cigarette filters (CFs) are a solid waste that is generated in large amounts owing to their low effective utilization. Globally, as many as 5.6 trillion CFs are reportedly discarded into the environment each year, which is a major threat to the environment (Novotny et al., 2009; Smith and Novotny, 2011). Numerous methods have been reported for recycling discarded CFs, such as electrospinning (Kakoria and Sinha-Ray, 2022), solution blow spinning (Tan et al., 2019), and centrifugal spinning (Xia et al., 2022), which are mainly used for air/water filtration (Kim and Park, 2022), heavy metal separation (Gupta et al., 2015), drug delivery (Khoshnevisan et al., 2018), and biosensing. The aforementioned applications show that acetate fiber possesses good hydrophilic properties (Xu and Na, 2020) and is biodegradable, providing a functional design for application to high-efficiency and stable solar desalination.
In this study, an eco-friendly and recyclable evaporator was assembled using acetylene carbon black (AC)-coated discarded CFs. The surface of AC coating provides excellent solar-absorbing properties and an effective water supply owing to the hydrophilic characteristics of the CF. The results show that the evaporator not only exhibits a significantly high evaporation rate (1.81 kg·m− 2·h− 1) but also possesses superior salt-rejection capability and cycling stability. Additionally, the AC-CF evaporator can be dissolved and recycled to alleviate environmental pressure. This strategy for recovering cellulose acetate CFs guides the use of renewable polymer resources from discarded CFs as photothermal evaporators.