1. Introduction
Construction operations on building sites are notorious sources of atmospheric pollution, generating varying degrees of dust pollution at different stages of construction, which adversely affects both human health and the ambient air quality [
1]. Dust refers to a general term for solid particles that can persist in the air for an extended period [
2]. Airborne dust often contains numerous toxic components, such as chromium, manganese, cadmium, lead, mercury, arsenic, and more [
3]. When individuals inhale dust, particularly particles smaller than 5 μm, these particles can easily penetrate deep into the lungs, causing toxic pneumonitis or silicosis, and, in some cases, even leading to lung cancer [
4]. Pollutants deposited in the lungs, once dissolved, directly enter the bloodstream, causing blood poisoning. Undissolved pollutants may also be absorbed by cells, leading to structural damage to the cells.
Existing research indicates that earthwork, specifically excavation and filling, is the most significant contributor to pollutant emissions throughout the entire construction process [
5]. Dust, characterized by its wide coverage and rapid dispersion, poses challenges in pollution control, as pollutants can remain suspended in the air for extended periods without settling [
6]. The issue of dust pollution control during construction operations urgently requires attention. Currently, mainstream dust control methods include electric dustproof technology, mist dust removal technology, and environmentally friendly dust suppressant technology, among others [
7].
Wang et al. [
8], by incorporating water-retaining agents and surfactants into binders, discovered a significant improvement in the hardness and water retention of the dust suppressant composite. Hu et al. [
9] formulated a frost-resistant dust suppressant, enhancing water retention performance by 88%. Yu et al. [
10] used humic acid (HA) and grafted acrylamide (AM) as the main raw material, grafting it to produce a dust suppressant for coal transportation, which showed non-corrosive properties.
With increasing environmental demands, dust suppressants are evolving towards functional composites, emphasizing green, environmentally friendly, and degradable characteristics [
11]. Eco-friendly composite chemical dust suppressants are composed of binders, water-absorbing agents, and water-retaining agents, each derived from environmentally friendly and degradable materials, thus avoiding secondary pollution [
12]. Feng et al. [
13] utilized peanut shells to prepare a highly effective and environmentally friendly novel degradable nanocellulose dust suppressant. Compared to traditional dust suppressants, eco-friendly composite dust suppressants offer more comprehensive functionality and longer-lasting dust suppression, with the added benefit of cost reduction. Tripathi and Sandha [
14] used polyvinyl alcohol as a monomer, ammonium persulfate as an initiator, aluminum hydroxide as a cross-linking agent, and glycerol as a plasticizer to prepare a polyvinyl alcohol-grafted cellulose-based sugarcane bagasse dust suppressant in a microwave reactor, significantly reducing production costs.
Compound dust suppressants have substantially reduced costs and can fundamentally address dust pollution issues on construction sites. For instance, Lee et al. [
15] utilized environmentally friendly methylcellulose-based polymers to investigate particulate matter reduction efficiency. Medeiros et al. [
16] used glycerol oligomerization to produce dust suppressants and the test results showed that hexa and heptaglycerol exhibited a good viscosity and dust suppression performance. Moreover, Gao et al. [
17] adopted the response surface method (RSM) to evaluate the dust reduction effect. The above studies provide scientific evidence to select the proposed materials and method for dust suppressant preparation in this study.
Therefore, this study aligns with the principles of green development and proposes the development of an eco-friendly composite chemical dust suppressant using hydroxyethyl cellulose (HEC), glycerol (C3H8O3), and isomeric tridecyl alcohol polyoxyethylene ether (AEO-13) as raw materials. This dust suppressant is designed to efficiently control dust through film binding, water retention, and high wetting properties, exhibiting multifunctionality. Through response surface methodology, a response surface model is established to analyze the interrelationships and degrees of influence among various components, thereby obtaining the optimal mixing ratio of dust suppressant components. The feasibility of dust suppression is verified through microscopic characterization, compositional analysis, and practical applications at construction sites, providing a new approach to the prevention and control of dust pollution at construction sites.
2. Experimental Program
2.1. Raw Materials
Materials used in this experiment include hydroxyethyl cellulose, sodium polyacrylate, propylene glycol, triethanolamine, Sodium Dodecyl Sulfate, Sodium Dodecyl Benzene Sulfonate, and Isostearyl Alcohol Ethoxylate, all analytical grade. Reagents were purchased from Shandong Youso Chemical Technology Co., Ltd. (Linyi, China), Tianjin Kemiou Chemical Reagent Co., Ltd. (Tianjin, China), Changde Bickman Biotechnology Co., Ltd. (Changde, China), and Wuxi Jingke Chemical Co., Ltd. (Wuxi, China). RO water was prepared in house.
2.2. Test Instruments
The experimental apparatus includes an FA2004B electronic analytical balance from Foshan Nanbeihu E-Commerce Co., Ltd. (Foshan, China), an HN101-3 blast drying oven from Nantong Hunan Scientific Instrument Co., Ltd. (Nantong, China), an HJ-4A multi-head magnetic heating stirrer from Jinan Oulaibo Scientific Instrument Co., Ltd. (Jinan, China), an HHWZI-600 constant temperature and humidity water bath from Henan Shuli Instrument Co., Ltd. (Zhengzhou, China), a PHB-5 digital pH meter from Shanghai Yidian Scientific Instruments Co., Ltd (Shanghai, China), an NDJ-5S viscometer from Shanghai MiTong Mechanical and Electrical Technology Co., Ltd. (Shanghai, China), and an Apreo 2C scanning electron microscope from Shanghai Thermo Fisher Scientific Company (Shanghai, China). Additionally, several items, such as beakers, standard sieve screens, evaporating dishes, glass rods, etc., were also used.
2.3. Test Procedures
The developed dust suppressant in this study is intended for dust control in construction sites. Combining with the mechanism of dust suppressant agents, the specific experimental procedures are outlined as follows:
First are single-factor optimization experiments for the composite dust suppressant [
18]. Through single-factor experiments, adhesive agents, water-retaining agents, and surfactants are screened from various functional additives to formulate an environmentally friendly composite dust suppressant. The corresponding dust suppression performance data were used as screening indicators to explore the stability of the performance of each auxiliary agent and determine the optimal concentration range.
Second, orthogonal optimization experiments are based on response surface methodology. The viscosity agent, water-retaining agent, and surfactant selected from the single-factor experiments were used as independent variables. Viscosity, evaporation resistance, and permeability rate were taken as response values. A Box–Behnken model was established for experimental design, optimizing the values of each component of the dust suppressant [
19]. Subsequently, through variance analysis, two-factor interaction analysis, model validation, and experimental verification, the results showed good agreement between the predicted values of the model and the experimental values, proving that the calculated optimal ratio of the model is reasonable and effective.
Third, characterization of the dust suppressant properties and wind erosion resistance testing [
20]. Property characterization includes pH value, surface tension, viscosity, determination of toxic and harmful substances, and SEM scanning electron microscope microscopic morphology analysis. A comprehensive evaluation was conducted from both the physicochemical indicators including viscosity, water retention rate, surface tension, and morphological characteristics of the dust suppressant. Wind erosion resistance testing aimed to demonstrate the ability of the composite dust suppressant to withstand adverse weather conditions. The experimental method flowchart is presented in
Figure 1.
3. Selection of Dust Suppressant Raw Materials
3.1. Selection and Treatment of Soil Samples
The experimental test conducted a sampling survey at a construction site [
20]. The sampling method followed the snake-shaped sampling technique used in soil sampling, with a total of nine sampling points established [
21]. A specific area in the construction site was chosen, and sampling points were evenly distributed in a “Z” pattern. During sampling, the surface soil within a 5-square-meter area around each sampling point was swept with a broom and collected in a soil collection cylinder. After sampling all nine points, the collected samples were transported back to the laboratory for further use.
For dust sample processing, larger particles such as sand, gravel, dry branches, and plastic waste were initially removed as construction debris. Subsequently, the dust samples underwent grinding treatment. The ground dust samples were sieved through a 100-mesh standard sieve, and the sieved dust was dried in a constant-temperature forced-air drying oven at 105 °C for 8 h. Afterward, the samples were cooled to room temperature in a drying chamber, weighed, packaged, and stored for future use.
3.2. Optimal Selection of Binder
The bond strength test is a crucial indicator for evaluating the dust suppression effectiveness of dust suppressants. Some scholars, when optimizing binders, have utilized hydroxyethyl cellulose and sodium polyacrylate separately to formulate dust suppressants. Both hydroxyethyl cellulose [
22] and sodium polyacrylate [
23] exhibit excellent bonding properties without causing environmental pollution. Therefore, building upon this foundation, this experiment further optimized between the two materials. Hydroxyethyl cellulose and sodium polyacrylate solutions were prepared with concentration gradients of 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by mass. Viscosity measurements and temperature sensitivity tests were conducted to optimize these materials as binders for the composite dust suppressant. The viscosity measurement results are depicted in
Figure 2.
Viscosity measurements were conducted for hydroxyethyl cellulose and sodium polyacrylate, and the results are presented in
Figure 1. At a mass concentration of 0.05%, the viscosity of hydroxyethyl cellulose is 2.73 mPa·s, which increases to 137.48 mPa·s as the mass concentration rises to 0.5%. Higher viscosity values promote particle aggregation, but for practical spraying convenience, a moderate viscosity is desirable. Hence, hydroxyethyl cellulose concentrations in the range of 0.2% to 0.4% were selected for response surface optimization analysis.
Additionally, it was observed that at a mass concentration of 0.05%, the viscosity of sodium polyacrylate is 22.8 mPa·s, reaching 297.7 mPa·s as the mass concentration increases to 0.5%. Sodium polyacrylate exhibits good bonding properties at lower concentrations but experiences reduced sprayability at higher concentrations, diminishing its practicality.
Subsequently, this study conducted temperature sensitivity tests on hydroxyethyl cellulose and sodium polyacrylate. Temperature, serving as the sole independent variable, was set at gradients of 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, and 45 °C. Test experiments were carried out using solutions of hydroxyethyl cellulose and sodium polyacrylate with a mass concentration midpoint of 0.3% from the previously mentioned concentration gradients. The experimental results are presented in
Figure 3.
From the temperature sensitivity test results, it can be observed that as the temperature increases, molecular movement accelerates, leading to a decrease in viscosity. The viscosity of hydroxyethyl cellulose solution decreases from 31.27 mPa·s to 19.2 mPa·s, while the viscosity of sodium polyacrylate solution decreases from 138.77 mPa·s to 118.1 mPa·s. It is evident that the hydroxyethyl cellulose solution is more stable in high-temperature environments. Since this dust suppressant is primarily intended for outdoor open spaces with varying temperatures during outdoor operations, a concentration range of 0.2% to 0.4% for hydroxyethyl cellulose was ultimately selected as the binder for the environmentally friendly composite dust suppressant for further response surface optimization analysis.
3.3. Optimal Selection of Water-Retaining Agent
Water retention performance is also a crucial indicator for assessing dust suppression effectiveness. In this study, we selected two commonly used water-retaining agents, glycerol and triethanolamine. Solutions of triethanolamine and glycerol were prepared with mass concentrations of 0.01%, 0.05%, 0.1%, 0.5%, 1%, and 3%. Additionally, a control experiment using plain water was set up. Using a spraying quantity of 15 mL, the prepared water-retaining agent solutions were sprayed onto aluminum boxes containing soil samples. Subsequently, the aluminum boxes were left to naturally evaporate under room temperature conditions. The experimental results are presented in
Table 1 and
Table 2.
From the water retention rate results of glycerol and triethanolamine, it can be observed that the water retention rate of the 3% glycerol solution after 144 h is 12.83%, while the water retention rate for the control group with plain water is only 2.37% after 144 h. The water retention rate depends on the water-absorbing capacity of the water-retaining agent, and particles infiltrated with water are less likely to become airborne in the atmosphere. Glycerol exhibits excellent water retention capacity, and when the mass concentration exceeds 3%, the water retention rate of glycerol stabilizes at around 13%. Therefore, the concentration range of 1% to 3% was selected for response surface optimization. Additionally, the water retention rate of the 3% triethanolamine solution after 144 h is 9.1%, which is higher than the control group with plain water but inferior to the glycerol solution in terms of water retention performance. Hence, glycerol solution was chosen as the water-retaining agent for the environmentally friendly composite dust suppressant.
3.4. Optimal Selection of Surfactant
The primary reason for choosing surfactants is based on their excellent wetting and emulsifying properties, effectively reducing the surface tension of the dust suppressant solution. When surfactants are dissolved in water, the hydrophilic groups facing the water side reduce the surface tension of the solution, enhancing the ability of the composite dust suppressant to wet the dust. The hydrophobic groups on the opposite side facing away from water form the interfacial adsorption forces that can effectively capture airborne dust particles. Additionally, due to their emulsifying effect, the solution of the composite dust suppressant disperses well and is less prone to precipitation, facilitating spraying [
24]. For these reasons, this experiment selected three surfactants with good wetting and emulsifying properties—Isotridecanol Polyethylene Glycol Ether (M1), Sodium Dodecyl Sulfate (M2), and Sodium Dodecyl Benzene Sulfonate (M3)—to conduct surface tension testing. The test results are shown in
Figure 4.
From
Figure 4, it can be observed that Isotridecanol Polyethylene Glycol Ether (M1) reaches a surface tension of 29.5 mN/m at a mass concentration of 0.5%. A lower surface tension indicates better wetting performance, leading to improved dust suppression performance in practical applications. Additionally, after the mass concentration of Isotridecanol Polyethylene Glycol Ether (M1) reaches 0.5%, the surface tension stabilizes around 29.5 mN/m. Therefore, for the dust suppressant, Isotridecanol Polyethylene Glycol Ether (M1) was chosen as the surfactant, and the concentration range of 0.5% to 1% was selected for response surface optimization.