Adsorption of sunscreen compounds from wastewater using commercial activated carbon: detailed kinetic and thermodynamic analyses

Sunscreen compounds are one of the most toxic substances detected in the aqueous
environment. However, these molecules are continuously utilized in a various range of products
to provide protection against UV radiation. The removal of three sunscreen compounds, 4-
hydroxybenzophenone (4-HBP), 2,4-dihydroxybenzophenone (BP-1) and oxybenzone (BP-3), by
commercial activated carbon (AC) was investigated using batch adsorption experiments. Different
operational characteristics, such as adsorbent dosing, interaction time, solution pH and starting
sunscreen compound concentration, were studied. The adsorption capacity of the AC material was
assessed using a liquid chromatograph associated with a mass spectrometer detector (LC–MS/MS).
Two isotherm models were utilized to explained the target compound adsorption phenomenon
(Langmuir and Freundlich), while pseudo-first and -second kinetic orders and thermodynamics were
utilized to examine the adsorption mechanism. The maximum adsorption capacities determined from
the Langmuir isotherms were established as 43.8 mg/g for 4-HBP, 48.8 mg/g for BP-3 and 41.1 mg/g
for BP-1. The thermodynamic parameters revealed the following: a negative DG (<20 KJ/mol)
and DH and a positive DS of the targeted sunscreen compounds adsorbed onto AC suggest a
spontaneous and exothermic adsorption process, favored by lower temperature, proving that the
physical sorption mechanism prevailed. Effective adsorption of 4-HBP, BP-3 and BP-1 from real
wastewater samples proved the viability of sunscreen compound removal using commercial AC
material. This paper offers promising results on a sustainable, economical and environmentally
friendly method for removal of ubiquitous sunscreen compounds from wastewater, as a possible
enhancement of treatment processes.