Question: What did Bekenstein propose about black holes?
About the article "Black hole", section "Entropy and thermodynamics".

Candidate passages:
In 1972, Bekenstein was the first to suggest that black holes should have a well-defined entropy.
Bekenstein also formulated the generalized second law of thermodynamics, black hole thermodynamics, for systems including black holes.
Both contributions were affirmed when Stephen Hawking proposed the existence of Hawking radiation two years later.
Hawking had initially opposed Bekenstein's idea.
Based on his black-hole thermodynamics work, Bekenstein also demonstrated the Bekenstein bound: there is a maximum to the amount of information that can potentially be stored in a given finite region of space which has a finite amount of energy (which is similar to the holographic principle).
In 1982, Bekenstein was the first person to develop a rigorous framework to generalize the laws of electromagnetism to handle inconstant physical constants.
His framework replaces the fine structure constant by a scalar field.
However, this framework for changing constants did not incorporate gravity.
In 2004, Bekenstein greatly boosted Mordehai Milgrom’s theory of Modified Newtonian Dynamics (MOND) by developing a relativistic version.
It is known as TeVeS for Tensor/Vector/Scalar and it introduces three different fields in space time to replace the one gravitational field. 
  J. D. Bekenstein, "Information in the Holographic Universe".
Scientific American, Volume 289, Number 2, August 2003, p. 61.
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Physical applications of LQG.
Black hole entropy.
The Immirzi parameter (also known as the Barbero-Immirzi parameter) is a numerical coefficient appearing in loop quantum gravity.
It may take real or imaginary values.
Black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons.
The no hair conjecture of general relativity states that a black hole is characterized only by its mass, its charge, and its angular momentum; hence, it has no entropy.
It appears, then, that one can violate the second law of thermodynamics by dropping an object with nonzero entropy into a black hole.
Work by Stephen Hawking and Jacob Bekenstein showed that one can preserve the second law of thermodynamics by assigning to each black hole a "black-hole entropy" formula_325 where "A" is the area of the hole's event horizon, "k"B is the Boltzmann constant, and "ℓ"P = is the Planck length.
The fact that the black hole entropy is also the maximal entropy that can be obtained by the Bekenstein bound (wherein the Bekenstein bound becomes an equality) was the main observation that led to the holographic principle.
An oversight in the application of the no-hair theorem is the assumption that the relevant degrees of freedom accounting for the entropy of the black hole must be classical in nature; what if they were purely quantum mechanical instead and had non-zero entropy?
Actually, this is what is realized in the LQG derivation of black hole entropy, and can be seen as a consequence of its background-independence - the classical black hole spacetime comes about from the semi-classical limit of the quantum state of the gravitational field, but there are many quantum states that have the same semiclasical limit.
Specifically, in LQG it is possible to associate a quantum geometrical interpretation to the microstates: these are the quantum geometries of the horizon which are consistent with the area, A, of the black hole and the topology of the horizon (i.e.
spherical).
LQG offers a geometric explanation of the finiteness of the entropy and of the proportionality of the area of the horizon.
These calculations have been generalized to rotating black holes.
It is possible to derive, from the covariant formulation of full quantum theory (Spinfoam) the correct relation between energy and area (1st law), the Unruh temperature and the distribution that yields Hawking entropy.
The calculation makes use of the notion of dynamical horizon and is done for non-extremal black holes.
A recent success of the theory in this direction is the computation of the entropy of all non singular black holes directly from theory and independent of Immirzi parameter.
The result is the expected formula formula_326, where S is the entropy and A the area of the black hole, derived by Bekenstein and Hawking on heuristic grounds.
This is the only known derivation of this formula from a fundamental theory, for the case of generic non singular black holes.
Older attempts at this calculation had difficulties.
The problem was that although Loop quantum gravity predicted that the entropy of a black hole is proportional to the area of the event horizon, the result depended on a crucial free parameter in the theory, the above mentioned Immirzi parameter.
However, there is no known computation of the Immirzi parameter, so it had to be fixed by demanding agreement with Bekenstein and Hawking's calculation of the black hole entropy.
Carlo Rovelli and Francesca Vidotto have proposed that in the interior of a black hole is a planck star based on LQG physics rather than a singularity proposed by general relativity, and resolves the black hole information paradox. 
Black holes.
It happens that the Bekenstein-Hawking Entropy of three-dimensional black holes exactly saturates the bound formula_5 where "A" is the two-dimensional area of the black hole's event horizon in units of the Planck area, formula_6.
The bound is closely associated with black hole thermodynamics, the holographic principle and the covariant entropy bound of quantum gravity, and can be derived from a conjectured strong form of the latter. 
Bekenstein derived the bound from heuristic arguments involving black holes.
If a system exists that violates the bound, i.e.
by having too much entropy, Bekenstein argued that it would be possible to violate the second law of thermodynamics by lowering it into a black hole.
In 1995, Ted Jacobson demonstrated that the Einstein field equations (i.e., general relativity) can be derived by assuming that the Bekenstein bound and the laws of thermodynamics are true.
However, while a number of arguments have been devised which show that some form of the bound must exist in order for the laws of thermodynamics and general relativity to be mutually consistent, the precise formulation of the bound has been a matter of debate.