*Article* **Uptake of BF Dye from the Aqueous Phase by CaO-g-C3N<sup>4</sup> Nanosorbent: Construction, Descriptions, and Recyclability**

**Ridha Ben Said 1,2,\*, Seyfeddine Rahali <sup>1</sup> , Mohamed Ali Ben Aissa <sup>1</sup> , Abuzar Albadri <sup>3</sup> and Abueliz Modwi <sup>1</sup>**

	- <sup>3</sup> Department of Chemistry, College of Science, Qassim University, Buraydah 52571, Saudi Arabia
	- **\*** Correspondence: 141255@qu.edu.sa

**Abstract:** Removing organic dyes from contaminated wastewater resulting from industrial effluents with a cost-effective approach addresses a major global challenge. The adsorption technique onto carbon-based materials and metal oxide is one of the most effective dye removal procedures. The current work aimed to evaluate the application of calcium oxide-doped carbon nitride nanostructures (CaO-g-C3N<sup>4</sup> ) to eliminate basic fuchsine dyes (BF) from wastewater. CaO-g-C3N<sup>4</sup> nanosorbent were obtained via ultrasonication and characterized by scanning electron microscopy, X-ray diffraction, TEM, and BET. The TEM analysis reveals 2D nanosheet-like nanoparticle architectures with a high specific surface area (37.31 m2/g) for the as-fabricated CaO-g-C3N<sup>4</sup> nanosorbent. The adsorption results demonstrated that the variation of the dye concentration impacted the elimination of BF by CaO-C3N<sup>4</sup> while no effect of pH on the removal of BF was observed. Freundlich isotherm and Pseudo-First-order adsorption kinetics models best fitted BF adsorption onto CaO-g-C3N<sup>4</sup> . The highest adsorption capacity of CaO-g-C3N<sup>4</sup> for BF was determined to be 813 mg. g−<sup>1</sup> . The adsorption mechanism of BF is related to the π-π stacking bridging and hydrogen bond, as demonstrated by the FTIR study. CaO-g-C3N<sup>4</sup> nanostructures may be easily recovered from solution and were effectively employed for BF elimination in at least four continuous cycles. The fabricated CaO-g-C3N<sup>4</sup> adsorbent display excellent BF adsorption capacity and can be used as a potential sorbent in wastewater purification.

**Keywords:** calcium oxide-doped carbon nitride nanostructures; basic fuchsine; elimination mechanism; π-π stacking

#### **1. Introduction**

Water pollution is one of the most important environmental hazards in the modern world, caused by wastewater discharge, insufficient treatment methods, and leakage into the natural water cycle [1,2]. Depending on the source, such as industrial plants, wastewater streams can contain excessively polluting components. Organics [3] (phenolic compounds, dyes, halogenated compounds, oils, etc.) and heavy metals (Hg, Cd, Pb, Cr, Ag, etc.) [4] are potential contaminants in wastewater, as they are biodegradable, volatile, and recycled organic compounds, suspended particles, pathogens, and parasites. Most chemical dyes are probable carcinogens [5]. Thus, before discharging wastewater, it is important to lessen or remove the presence of these potentially fatal substances.

Among these dyes, basic fuchsin BF is a triarylmethane dye that is inflammable and has antibacterial and fungicidal characteristics [6,7]. It is commonly employed as a colorant in textile and leather goods as well as in the staining of collagen and tubercle bacillus [8]. Because of its low biodegradability and its toxicity, carcinogenicity, and unsightliness [9–11], Basic Fuchsin removal from wastewater systems is a major concern that should be studied and executed as soon as possible.

**Citation:** Said, R.B.; Rahali, S.; Ben Aissa, M.A.; Albadri, A.; Modwi, A. Uptake of BF Dye from the Aqueous Phase by CaO-g-C3N<sup>4</sup> Nanosorbent: Construction, Descriptions, and Recyclability. *Inorganics* **2023**, *11*, 44. https://doi.org/10.3390/ inorganics11010044

Academic Editor: Roberto Nisticò

Received: 5 November 2022 Revised: 9 January 2023 Accepted: 11 January 2023 Published: 16 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

In addition to the traditional biological, electrochemical, and photocatalytic oxidation and decomposition routes, physical processes (such as adsorption) are common methods that have also been developed and are used to remove organic pollutants from wastewater streams [12–14]. Even though these technologies can turn organic pollutants into nonhazardous molecules and can be used in various ways, their inability to be scaled up is a significant problem from an engineering point of view.

More specifically, the adsorption method was widely regarded as the most effective way to treat dye wastewater because of its significant adsorption capacity, low cost, good selectivity, and ease of operation [15–18]. Therefore, many researchers invest a lot of time and effort into creating new adsorbents, as well as adsorption mechanisms and treatment technology, in the hopes that they would be more useful in the treatment of dye wastewater [19–21].

Besides, graphitic carbon nitride (g-C3N4) nanosheet has been identified as an indispensable material for two-dimensional structures due to its graphitic-like structure and high stability under ambient circumstances [22]. It is composed of carbon and nitrogen and is most commonly employed for energy conversion and storage. Its π conjugated polymeric metal-free semiconducting 2D structure is composed of graphitic planes composed of sp2-hybridized carbon and nitrogen [23]. Because g-C3N<sup>4</sup> contains a sufficient number of edge amino and amino groups (NH/NH2), it can supply several binding sites. Therefore, g-C3N<sup>4</sup> is regarded as a suitable adsorbent for removing pollutants from wastewater. Nevertheless, g-C3N<sup>4</sup> nanosheets capability to adsorb is limited by its small surface area and few functional groups [24].

Therefore, the development of g-C3N4-containing compounds with higher photonic efficiency, such as TiO<sup>2</sup> and ZnO, piqued the curiosity of a vast number of researchers [25,26]. This was accomplished by combining g-C3N<sup>4</sup> with another semiconductor and decorating g-C3N<sup>4</sup> with noble metals [27–31]. Construction of heterojunctions comprised of g-C3N<sup>4</sup> mixed with another type of compound, such as CaO nanomaterials, and preparation of a Ca-O doped with g-C3N<sup>4</sup> with an improved surface texture by selecting the optimal preparation method are the most beneficial means of enhancing the adsorption properties of g-C3N4.

In the current study, a mesoporous CaO@g-C3N<sup>4</sup> nanocomposite was successfully produced using a simple sonochemical process and evaluated as a promising adsorbent material for adsorbing the basic fuchsin dye from a contaminated aqueous phase. The physicochemical relationship between characterizations and measurements of equilibrium and kinetics was studied. Adsorption isotherm data were also modeled, and the adsorption performance of CaO@g-C3N<sup>4</sup> nanocomposite for basic fuchsin was investigated.

#### **2. Experimental**

#### *2.1. Chemicals*

Sodium hydroxide (NaOH, ≥99%), sodium chloride (NaCl, ≥99%), basic fuchsin (BF, ≥85%), urea (CH4N2O, ≥98%) and calcium carbonate (CaCO3, ≥99%) purchased from Merck Company were used without further purification. The required dyes concentrations (25, 50, 100, 150, 200, and 300 ppm) were obtained by diluting BF stock solution (500 ppm).
