Mesoporous Activated Carbon from Leaf Sheath Date Palm Fibers by Microwave-Assisted Phosphoric Acid Activation for Efficient Dye

Mesoporous Activated Carbon from Leaf Sheath Date Palm Fibers by Microwave-Assisted Phosphoric Acid Activation for Efficient Dye Adsorption

1. INTRODUCTION

 Water contamination with textile dyes from industrial effluents has been one of the never-ending global issues. Dyes that bypass the inefficient wastewater treatment in textile industries enter the environment and cause harm to living organisms.1,2 According to,3 dyes are extensively utilized in many industrial activities namely paper, magazines, foods, cosmetics, leather, and much more. Therefore, it is not a surprise that the annual generation of dyes contained in wastewater from the textile industry alone has reached 2.15 billion tons.4,5 Based on the solubility properties, dyes can be grouped into soluble dyes (acidic, basic, reactive, and direct dyes) and insoluble dyes (vat, sulfur, disperse, and pigment dyes).6,7 According to,8 soluble dyes are harder to be removed due to their strong affinity toward the polar region of water molecules. Remazol Brilliant Blue R (RBBR) is one of the popular dyes in the textile industry, and it falls in the group of reactive dyes. Reactive dyes dissociate in water to produce negative ions (anionic dyes) and attach to the fiber substrate via covalent bonds. Up to 70% of the reactive dyes share similar characteristics of having at least one azo bridge (−N�N−) on their molecular structure.9 It is an absolute need for researchers to treat reactive dyes in wastewater since this classof dyes ends up in discharged effluents, most of which are around 10−50%.10 Activated carbon (AC) is a versatile and reliable adsorbent for treating a wide range of water-based pollutants such as dyes,11−14 heavy metals,15−18 antibiotics,19,20 pesticides,21,22 and much more. This outstanding trait of AC is attributed to two main factors: (i) high surface area from a highly porous structure and (ii) the existence of many polar functional groups that enhance the attraction between adsorbate molecules and the AC’s surface. However, two decades ago, AC was struggling with the issue of high production costs due to the usage of the nonrenewable precursors coal, lignite, and petroleum coke.8 Alternatively, researchers have been actively producing AC from agricultural wastes such as Gelidiella acerosa seaweed,11 durian peel,8 peanut shell,23 coconut shell,21 biomass sludge,24 and alpinia galanga stem.25 Date palm (Pheonix dactylifera L.) is a native tree of the Middle East andNorth African countries, which contribute 88.90% (7,267,316 tons) of the global date fruit production. Other parts of the world such as America and Europe produce 0.58 and 0.18%, respectively.26 In addition to fruit production, the date palm tree also generates approximately 6 million tons of waste annually.27 According to,28 one date palm tree produces about 2−3 kg of dried leaf. Due to the low nitrogen percentage, these wastes are not suitable to be transformed into compost fertilizer, and incinerating them would cause catastrophic air pollution.29 Therefore, in this study, an attempt was made to transform leaf sheath date palm fibers (LSD) into AC via phosphoric acid chemical treatment, followed by microwave heating. Unlike a conventional furnace that works based on conduction heat transfer, microwave heating is more efficient, as it converts electromagnetic waves into thermal energy in a volumetric state; thus, the heating process can be done way faster.30 2. MAT

2. MATERIALS AND METHODS

2.1. Materials. Phosphoric acid (H3PO4) was obtained from Sigma-Aldrich, 0.10 M hydrochloric acid (HCl) was obtained from R&M Chemicals, and RBBR dye was purchased from Merck. Nitrogen in the form of N2 gas with a purity of 99.9% was supplied by MOX Gases Berhad. 2.2. Collection and Preparation of Leaf Sheath Date Palm Fiber-Activated Carbon. Raw leaf sheath date palm fibers (LSD) were collected from a farm near Riyadh city, Saudi Arabia, dried in the open air, chopped into small pieces, and finely ground to pass a 2.0 mm sieve. Then, it was brought to the lab and cleaned properly using tap water and then dried in an oven for 48 h at a temperature of 110 °C. The LSD was impregnated with H3PO4 at an impregnation ratio (IR) of 1:3 for 8 h at a temperature of 40 °C. Then, the impregnated LSD was loaded inside a quartz test tube and carbonized using a microwave oven (EMW2001W, Sweden) under the flow of N2 gas at a radiation power and radiation time of 616 W and 10 min, respectively. The activated LSD was soaked with 0.10 HCl for 30 min, then followed by a washing step until the washing water reached a pH of 6−7. Then, the sample was dried in an oven once again. After that, the dried sample (LSDAC) was stored in an airtight container until used in adsorption studies. 2.3. Characterization Methods. The samples in this study were characterized in terms of surface area (BET and Langmuir) and average pore diameter together with total pore volume utilizing a volumetric adsorption analyzer (Micromeritics ASAP 2020), scanning electron microscopy (SEM) images using a scanning electron microscope (LEO SUPRA 55VP, Germany), elemental analysis using a simultaneous thermal analyzer (Model PerkinElmer STA 6000), proximate analysis using a thermogravimetric analyzer, functional groups through a Fourier transform infrared spectrometer (FTIR) (IR Prestige 21 Shimadzu, Japan) and distribution of ζ-potential via a ζ-potential analyzer (Zetasizer Nano Series DKSH). 2.4. Equilibrium Study. In the equilibrium study, the influence of dissimilar adsorbate initial concentrations, the influence of adsorbate solution temperature, and the influence of adsorbate solution pH were verified. To understand the adsorbent performance under the various initial concentrations of the adsorbate solution, RBBR solution with six different concentrations between 25 and 300 mg/L were made and placed inside conical flasks. These flasks were shaken at 30 rpm in a water bath shaker. A total of 0.2 g of LSDAC was droppedinside each one of these flasks, and other conditions such as solution pH and solution temperature were fixed at the original pH and 30 °C, respectively. The determination of RBBR’s concentration was made via UV−vis spectrophotometry (Agilent Cary 60) every 15 min until equilibrium was reached. The wavelength for RBBR was set to 590 nm. To verify the effect of solution temperature, the temperature of the RBBR solution was varied between 30, 40, and 50 °C, while its pH remained unaltered. Meanwhile, the impact of solution pH on the adsorption process was verified by preparing the RBBR solution with six dissimilar pH values, ranging from 3 to 13, by adding NaOH/HCl, while the solution temperature remained unchanged at 30 °C. In these studies, (effect of solution temperature and solution pH), other parameters such as LSDAC weight, the concentration of the solution, the volume of the solution, and shaking speed were fixed at constant values of 0.2 g, 100 mg/L, 200 mL, and 30 rpm, respectively. RBBR uptakes and percentage removal were calculated based on the following equations, respectively Under the waft of N2 fuel at a radiation energy and radiation time of 616 W and 10 min, respectively. The activated LSD become soaked with zero.10 HCl for 30 min, then followed by means of a showering step till the showering water reached a pH of 6−7. Then, the sample became dried in an oven yet again. After that, the dried sample (LSDAC) was saved in an hermetic box till utilized in adsorption studies. 2.Three. Characterization methods. The samples in this study were characterised in phrases of surface location (bet and Langmuir) and average pore diameter together with general pore quantity utilising a volumetric adsorption analyzer (Micromeritics ASAP 2020), scanning electron microscopy (SEM) photos the usage of a scanning electron microscope (LEO SUPRA 55VP, Germany), elemental evaluation the usage of a simultaneous thermal analyzer (model PerkinElmer STA 6000), proximate evaluation the usage of a thermogravimetric analyzer, functional groups thru a Fourier transform infrared spectrometer (FTIR) (IR prestige 21 Shimadzu, Japan) and distribution of ζ-ability via a ζ-capacity analyzer (Zetasizer Nano collection DKSH). 2.Four. Equilibrium have a look at. Inside the equilibrium look at, the have an effect on of numerous adsorbate preliminary concentrations, the affect of adsorbate answer temperature, and the have an impact on of adsorbate answer pH were demonstrated. To understand the adsorbent overall performance beneath the various preliminary concentrations of the adsorbate answer, RBBR answer with six specific concentrations among 25 and three hundred mg/L have been made and positioned inner conical flasks. Those flasks have been shaken at 30 rpm in a water bathtub shaker. A total of zero.2 g of LSDAC changed into droppedinside each the sort of flasks, and different conditions inclusive of answer pH and solution temperature were fixed on the unique pH and 30 °C, respectively. The willpower of RBBR’s concentration became made thru UV−vis spectrophotometry (Agilent Cary 60) every 15 min till equilibrium became reached.