Isotherm, kinetics and ANN analysis of methylene blue adsorption onto nitrogen doped Ulva lactuca Biochar

Abstract

This study investigates the removal of methylene blue (MB) dye from aqueous solutions using a novel adsorbent, green algae (Ulva lactuca)-derived biochar-ammonia (NDULB), produced through activation with 85% sulfuric acid and hydrothermal treatment with ammonium hydroxide. The characterization of NDULB was carried out through various techniques, including BET surface area analysis and scanning electron microscopy, confirming its high surface area and effective porosity for dye adsorption. This work thoroughly examines the effects of initial MB dye concentration, solution pH, contact time, and NDULB dose on adsorption. The adsorption data were modeled using Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich isotherms, with the Freundlich model showing the best fit, indicating multilayer adsorption on a heterogeneous surface. According to the investigation's findings, with an initial MB concentration of 200 ppm and an NDULB dosage of 1.25 g L^-1, the adsorption capacity at equilibrium (q_e) is 966.31 mg g^-1. Kinetic analysis revealed that the pseudo-second-order model provided the best fit for the experimental data, suggesting chemisorption as the dominant adsorption mechanism. The artificial neural network modeling has been studied and reported. The study clarifies the effects of multiple variables on adsorption, which might lead to key insights to enlighten the development of effective wastewater treatment strategies. The study demonstrates that NDULB offers a promising, sustainable alternative for MB dye removal in wastewater treatment, with significant implications for large-scale application.

Keywords: Ulva lactuca; Adsorption; Ammonia-modified Biochar; Green algae; Methylene blue; Nitrogen-doped Biochar.

Fig. 1

Chemical structure of MB dye (basic blue 9; C.I.52015, λ_max = 665 nm, MF = C₁₆H₁₈N₃ClS.xH₂O, Mwt = 319.86 g/mole).

Fig. 2

Green algae U. lactuca (GAUL) FTIR graphs of SDULB and NDULB.

Fig. 3

(a) Drawing of N₂ Adsorption-Desorption, (b) Drawing of the BET, (c) The BJH adsorption drawing, and (d) The BJH desorption drawing of the SDULB (red) and NDULB (blue).

Fig. 4

SEM image of NDULB at ×1,000 (a) and ×25,000 magnification (b) at 20.0 kV.

Fig. 5

Diagrams showing TDA and TGA for GAUL, SDULB, and NDULB from 0 to 1000 °C.

Fig. 6

XRD diagram of synthesized SDULB and NDULB biochar.

Fig. 7

Overview of XPS spectrum of NDULB adsorbent with 1 eV resolution.

Fig. 8

Sorption of MB dye onto NDULB (a) zero point charge and (b) pH on the removal % of MB dye (MB dye = 100 ppm, adsorbent = 1.0 g L⁻¹, temperature = 25 °C).

Fig. 9

The removal of MB dye by NDULB (MB dye = (100–200 ppm), doses (0.50–1.50 g L⁻¹), and Temperature = 25 °C).

Fig. 10

The MB dye starting concentration (100–200 ppm) impact using NDULB doses (0.50–1.50 g L⁻¹) on q_e (mg g⁻¹) and temperature (25 °C).

Fig. 11

The impact of NDULB various doses (0.50–1.50 g L^–1) of different starting MB dye concentrations (100–200 ppm) (a) on removal %; (b) on q_e (mg g⁻¹), and temperature (25 °C).

Fig. 12

(a) Linearized LIM (b) FIM (c) TIM (d) DRIM isotherm profiles for MB dyes of initial concentration (100–200 ppm) on NDULB doses (0.50–1.50 g L⁻¹) and Temperature (25 °C).

Fig. 13

(a) PFOM, (b) PSOM, (c) EM, (d) IPDM, and (e) FDM kinetic models of adsorption of MB dye by NDULB adsorbent [starting MB dye concentration (100–200 ppm), NDULB dose (1.5 g L⁻¹), and Temperature (25 °C)].

Fig. 14

ANN architecture for MB dye adsorption.

Fig. 15

Datasets used for the LM algorithm’s training, validation, testing, and overall applications.

Fig. 16

LM algorithm performance.